common occurrence. There are, however, at many points hills which have
something of a kame-like character. There is such a hill a mile
southeast of the Court house at Baraboo, at the point marked p, Plate
XXXVII. In this hill there are good exposures which show its structure.
There are many hillocks of a general kame-like habit associated with the
terminal moraine south of the main quartzite range, and north of the
Wisconsin river. Many of them occur somewhat within the terminal moraine
a few miles northwest of Merrimac.
_B. Beyond the edge of the ice, on land._--As the waters escaping from
the ice flowed farther, deposits of stratified drift were made quite
beyond the edge of the ice. The forms assumed by such deposits are
various, and depended on various conditions. Where the waters issuing
from the edge of the ice found themselves concentrated in valleys, and
where they possessed sufficient load, and not too great velocity, they
aggraded the valleys through which they flowed, developing fluvial
plains of gravel and sand, which often extended far beyond the ice. Such
fluvial plains of gravel and sand constitute the _valley trains_ which
extend beyond the unstratified glacial drift in many of the valleys of
the United States. They are found especially in the valleys leading out
from the stouter terminal moraines of late glacial age. From these
moraines, the more extensive valley trains take their origin, thus
emphasizing the fact that they are deposits made by water beyond a
stationary ice margin. Valley trains have all the characteristics of
alluvial plains built by rapid waters carrying heavy loads of detritus.
Now and then their surfaces present slight variations from planeness,
but they are minor. Like all plains of similar origin they decline
gradually, and with diminishing gradient, down stream. They are of
coarser material near their sources, and of finer material farther away.
Valley trains constitute a distinct topographic as well as genetic type.
A perfect example of a valley train does not occur within the region
here discussed. There is such a train starting at the moraine where it
crosses the Wisconsin river above Prairie du Sac, and extending down
that valley to the Mississippi, but at its head this valley train is
wide and has the appearance of an overwash plain, rather than a valley
train. Farther from the moraine, however, it narrows, and assumes the
normal characteristics of a valley train. It is the gravel and sand of
this formation which underlies Sauk Prairie, and its topographic
continuation to the westward.
Where the subglacial streams did not follow subglacial valleys, they did
not always find valleys when they issued from the ice. Under such
circumstances, each heavily loaded stream coming out from beneath the
ice must have tended to develop a plain of stratified material near its
point of issue--a sort of alluvial fan. Where several such streams came
out from beneath the ice near one another, their several plains, or
fans, were likely to become continuous by lateral growth. Such border
plains of stratified drift differ from valley trains particularly (1) in
being much less elongate in the direction of drainage; (2) in being much
more extended parallel to the margin of the ice; and (3) in not being
confined to valleys. Such plains stood an especially good chance of
development where the edge of the ice remained constant for a
considerable period of time, for it was under such conditions that the
issuing waters had opportunity to do much work. Thus arose the type of
stratified drift variously known as _overwash plains_, _outwash plains_,
_morainic plains_, and _morainic aprons_. These plains sometimes skirt
the moraine for many miles at a stretch.
Overwash plains may sometimes depart from planeness by taking on some
measure of undulation, of the sag and swell (kame) type, especially near
their moraine edges. The same is often true of the heads of valley
trains. The heads of valley trains and the inner edges of overwash
plains, it is to be noted, occupy the general position in which kames
are likely to be formed, and the undulations which often affect these
parts of the trains and plains, respectively, are probably to be
attributed to the influence of the ice itself. Valley trains and
overwash plains, therefore, at their upper ends and edges respectively,
may take on some of the features of kames. Indeed, either may head in a
kame area.
Good examples of overwash or outwash plains may be seen at various
points in the vicinity of Baraboo. The plain west of the moraine just
south of the main quartzite ridge has been referred to under valley
trains. In Sauk Prairie, however, its characteristics are those of an
outwash plain, rather than those of a valley train.
[Illustration: Fig. 41.--The morainic or outwash plain bordering the
terminal moraine. The figure is diagrammatic, but represents, in cross
section, the normal relation as seen south of the quartzite range at the
east edge of Sauk Prairie, north of the Baraboo river and at some points
between the South range and the Baraboo.]
A good example of an outwash plain occurs southwest of Baraboo, flanking
the moraine on the west (Fig. 41). Seen from the west, the moraine just
north of the south quartzite range stands up as a conspicuous ridge
twenty to forty feet above the morainic plain which abuts against it.
Traced northward, the edge of the outwash plain, as it abuts against
the moraine, becomes higher, and in Section 4, Township 11 N., Range 6
E., the moraine edge of the plain reaches the crest of the moraine (Fig.
42). From this point north to the Baraboo river the moraine scarcely
rises above the edge of the outwash beyond.
[Illustration: Fig. 42.--The outwash plain is built up to the crest of
the moraine. The figure is diagrammatic, but this relation is seen at
the point marked W, Plate II.]
North of the Baraboo river the moraine is again distinct and the
overwash plain to the west well developed much of the way from the
Baraboo to Kilbourn City. A portion of it is known as Webster's Prairie.
Locally, the outwash plains of this region have been much dissected by
erosion since their deposition, and are now affected by many small
valleys. In composition these plains are nearly everywhere gravel and
sand, the coarser material being nearer the moraine. The loose material
is in places covered by a layer of loam several feet deep, which greatly
improves the character of the soil. This is especially true of Sauk
Prairie, one of the richest agricultural tracts in the state.
When the waters issuing from the edge of the ice were sluggish, whether
they were in valleys or not, the materials which they carried and
deposited were fine instead of coarse, giving rise to deposits of silt,
or clay, instead of sand or gravel.
At many points near the edge of the ice during its maximum stage of
advance, there probably issued small quantities of water not in the form
of well-defined streams, bearing small quantities of detritus. These
small quantities of water, with their correspondingly small loads, were
unable to develop considerable plains of stratified drift, but produced
small patches instead. Such patches have received no special
designation.
In the deposition of stratified drift beyond the edge of the ice, the
latter was concerned only in so far as its activity helped to supply the
water with the necessary materials.
_C. Deposits at and beyond the edge of the ice in standing water._--The
waters which issued from the edge of the ice sometimes met a different
fate. The ice in its advance often moved up river valleys. When at the
time of its maximum extension, it filled the lower part of a valley,
leaving the upper part free, drainage through the valley stood good
chance of being blocked. Where this happened a marginal valley lake was
formed. Such a lake was formed in the valley of the Baraboo when the
edge of the ice lay where the moraine now is (Plate II). The waters
which were held back by the ice dam, reinforced by the drainage from the
ice itself, soon developed a lake above the point of obstruction. This
extinct lake may be named Baraboo lake. In this lake deposits of
laminated clay were made. They are now exposed in the brick yards west
of Baraboo, and in occasional gullies and road cuts in the flat
bordering the river.
At the point marked s (Plate XXXVII) there was, in glacial
times, a small lake having an origin somewhat different from that of
Baraboo lake. The former site of the lake is now marked by
a notable flat. Excavations in the flat show that it is made up of
stratified clay, silt, sand and gravel, to the depth of many
feet,--locally more than sixty. These lacustrine deposits are well
exposed in the road cuts near the northwest corner of the flat, and in
washes at some other points. Plate XXXVIII shows some of the silt and
clay, the laminae of which are much distorted.
_Deltas_ must have been formed where well-defined streams entered the
lakes, and _subaqueous overwash plains_ where deltas became continuous
by lateral growth. The accumulation of stratified drift along the
ice-ward shores of such lakes must have been rapid, because of the
abundant supply of detritus. These materials were probably shifted about
more or less by waves and shore currents, and some of them may have been
widely distributed. Out from the borders of such lakes, fine silts and
clays must have been in process of deposition, at the same time that the
coarse materials were being laid down nearer shore.
[Illustration: WISCONSIN GEOL. AND NAT. HIST. SURVEY. BULLETIN NO. V.,
PL. XXXVIII.
Distorted laminae of silt and clay.]
Good examples of deltas and subaqueous overwash plains do not appear to
exist in the region, although conditions for their development seem to
have been present. Thus in the lake which occupied the valley of the
Baraboo, conditions would seem to have been ideal for the development of
such features; that is, the overwash plains previously described should,
theoretically, have been subaqueous overwash plains; but if this be
their character, their distinctive marks have been destroyed by
subsequent erosion.
During the maximum extension of an ice sheet, therefore, there was
chance for the development, at its edge or beyond it, of the following
types of stratified drift: (1) kames and kame belts, at the edge of the
ice; (2) fluvial plains or valley trains, in virtual contact with the
ice at their heads; (3) border plains or overwash plains, in virtual
contact with the ice at their upper edges; (4) ill-defined patches of
stratified drift, coarse or fine near the ice; (5) subaqueous overwash
plains and deltas, formed either in the sea or lakes at or near the edge
of the ice; (6) lacustrine and marine deposits of other sorts, the
materials for which were furnished by the waters arising from the ice.
So far as this region is concerned, all the deposits made in standing
water were made in lakes.
_Deposits Made by Extraglacial Waters During the Retreat of the Ice._
During the retreat of any ice sheet, disregarding oscillations of its
edge, its margin withdrew step by step from the position of extreme
advance to its center. When the process of dissolution was complete,
each portion of the territory once covered by the ice, had at some stage
in the dissolution, found itself in a marginal position. At all stages
in its retreat the waters issuing from the edge of the ice were working
in the manner already outlined in the preceding paragraphs. Two points
of difference only need be especially noted. In the first place the
deposits made by waters issuing from the retreating ice were laid down
on territory which the ice had occupied, and their subjacent stratum was
often glacial drift. So far as this was the case, the stratified drift
was super-morainic, not extra-morainic. In the second place the edge of
the ice in retreat did not give rise to such sharply marked formations
as the edge of the ice which was stationary. The processes which had
given rise to valley trains, overwash plains, kames, etc., while the ice
edge was stationary, were still in operation, but the line or zone of
their activity (the edge of the ice) was continually retreating, so that
the foregoing types, more or less dependent on a stationary edge, were
rarely well developed. As the ice withdrew, therefore, it allowed to be
spread over the surface it had earlier occupied, many incipient valley
trains, overwash plains, and kames, and a multitude of ill-defined
patches of stratified drift, thick and thin, coarse and fine. Wherever
the ice halted in its retreat, these various types stood chance of
better development.
Such deposits did not cover all the surface discovered by the ice in its
retreat, since the issuing waters, thanks to their great mobility,
concentrated their activities along those lines which favored their
motion. Nevertheless the aggregate area of the deposits made by water
outside the ice as it retreated, was great.
It is to be noted that it was not streams alone which were operative as
the ice retreated. As its edge withdrew, lakes and ponds were
continually being drained, as their outlets, hitherto choked by the ice,
were opened, while others were coming into existence as the depressions
in the surface just freed from ice, filled with water. Lacustrine
deposits at the edge of the ice during its retreat were in all essential
respects identical with those made in similar situations during its
maximum extension.
Disregarding oscillations of the ice edge at these stages, the deposits
made by extraglacial waters during the maximum extension of an ice
sheet, and during its retreat, were always left at the surface, so far
as the work of that ice sheet was concerned. The stratified drift laid
down by extraglacial waters in these stages of the last ice sheet which
affected any region of our continent still remain at the surface in much
the condition in which they were deposited, except for the erosion they
have since suffered. It is because of their position at the surface that
the deposits referable to these stages of the last ice sheet of any
given region have received most attention and are therefore most
familiar.
_Deposits Made by Extraglacial Waters During the Advance of the Ice._
During the advance of an ice sheet, if its edge forged steadily forward,
the waters issuing from it, and flowing beyond, were effecting similar
results. They were starting valley trains, overwash plains, kames, and
small ill-defined patches of stratified drift which the ice did not
allow them to complete before pushing over them, thus moving forward the
zone of activity of extraglacial waters. Unlike the deposits made by the
waters of the retreating ice, those made by the waters of the advancing
stage were laid down on territory which had not been glaciated, or at
least not by the ice sheet concerned in their deposition. If the ice
halted in its advance, there was at such time and place opportunity for
the better development of extraglacial stratified drift.
Lakes as well as streams were concerned in the making of stratified beds
of drift, during the advance of the ice. Marginal lakes were obliterated
by having their basins filled with the advancing ice, which displaced
the water. But new ones were formed, on the whole, as rapidly as their
predecessors became extinct, so that lacustrine deposits were making at
intervals along the margin of the advancing ice.
Deposits made in advance of a growing ice sheet, by waters issuing from
it, were subsequently overridden by the ice, to the limit of its
advance, and in the process, suffered destruction, modification, or
burial, in whole or in part, so that now they rarely appear at the
surface.
_Deposits Made by Subglacial Streams._
Before their issuance from beneath the ice, subglacial waters were not
idle. Their activity was sometimes erosive, and at such times stratified
deposits were not made. But where the sub-glacial streams found
themselves overloaded, as seems frequently to have been the case, they
made deposits along their lines of flow. Where such waters were not
confined to definite channels, their deposits probably took on the form
of irregular patches of silt, sand, or gravel; but where depositing
streams were confined to definite channels, their deposits were
correspondingly concentrated.
When subglacial streams were confined to definite channels, the same may
have been constant in position, or may have shifted more or less from
side to side. Where the latter happened there was a tendency to the
development of a belt or strip of stratified drift having a width equal
to the extent of the lateral migrations of the under-ice stream. Where
the channel of the subglacial stream remained fixed in position, the
deposition was more concentrated, and the bed was built up. If the
stream held its course for a long period of time, the measure of
building may have been considerable. In so far as these channel deposits
were made near the edge of the ice, during the time of its maximum
extension or retreat, they were likely to remain undisturbed during its
melting. The aggraded channels then came to stand out as ridges. These
ridges of gravel and sand are known as osars or eskers. It is not to
be inferred that eskers never originated in other ways, but it seems
clear that this is one method, and probably the principal one, by which
they came into existence. Eskers early attracted attention, partly
because they are relatively rare, and partly because they are often
rather striking topographic features. The essential conditions,
therefore, for their formations, so far as they are the product of
subglacial drainage, are (1) the confining of the subglacial streams to
definite channels; and (2) a sufficient supply of detritus. One esker
only has been found in the region under consideration. It is located at
the point marked j, Plate II, seven and one-half miles northeast of
Merrimac and one and one-half miles south of Alloa (g, Plate II). The
esker is fully a quarter of a mile long, about thirty feet high, and
four rods wide at its base.
Subglacial deposits of stratified drift were sometimes made on
unstratified drift (till) already deposited by the ice before the
location of the stream, and sometimes on the rock surfaces on which no
covering of glacier drift had been spread.
It is to be kept in mind that subglacial drainage was operative during
the advance of an ice sheet, during its maximum extension, and during
its retreat, and that during all these stages it was effecting its
appropriate results. It will be readily seen, however, that all deposits
made by subglacial waters, were subject to modification or destruction
or burial, through the agency of the ice, and that those made during the
advance of the ice were less likely to escape than those made during its
maximum extension or retreat.
RELATIONS OF STRATIFIED TO UNSTRATIFIED DRIFT.
When it is remembered that extraglacial and subglacial waters were
active at all stages of an ice sheet's history, giving rise, or tending
to give rise to all the phases of stratified drift enumerated above;
when it is remembered that the ice of several epochs affected much of
the drift-covered country; and when it is remembered further that the
edge of the ice both during advance and retreat was subject to
oscillation, and that each advance was likely to bury the stratified
drift last deposited, beneath unstratified, it will be seen that the
stratified drift and the unstratified had abundant opportunity to be
associated in all relationships and in all degrees of intimacy, and that
the relations of the one class of drift to the other may come to be very
complex.
As a result of edge oscillation, it is evident that stratified drift may
alternate with unstratified many times in a formation of drift
deposited during a single ice epoch, and that two beds of till,
separated by a bed of stratified drift, do not necessarily represent two
distinct glacial epochs. The extent of individual beds of stratified
drift, either beneath the till or inter-bedded with it, may not be
great, though their aggregate area and their aggregate volume is very
considerable. It is to be borne in mind that the ice, in many places,
doubtless destroyed all the stratified drift deposited in advance on the
territory which it occupied later, and that in others it may have left
only patches of once extensive sheets. This may help to explain why it
so frequently happens that a section of drift at one point shows many
layers of stratified drift, while another section close by, of equal
depth, and in similar relationships, shows no stratified material
whatsoever.
Such deposits as were made by superglacial streams during the advance of
the ice must likewise have been delivered on the land surface, but would
have been subsequently destroyed or buried, becoming in the latter case,
submorainic. This would be likely to be the fate of all such
superglacial gravels as reached the edge of the ice up to the time of
its maximum advance.
Streams descending from the surface of the ice into crevasses also must
have carried down sand and gravel where such materials existed on the
ice. These deposits may have been made on the rock which underlies the
drift, or they may have been made on stratified or unstratified drift
already deposited. In either case they were liable to be covered by
till, thus reaching an inter-till or sub-till position.
Englacial streams probably do little depositing, but it is altogether
conceivable that they might accumulate such trivial pockets of sand and
gravel as are found not infrequently in the midst of till. The
inter-till position would be the result of subsequent burial after the
stratified material reached a resting place.
Complexity of relations.--From the foregoing it becomes clear that
there are diverse ways by which stratified drift, arising in connection
with an ice sheet, may come to be interbedded with till, when due
recognition is made of all the halts and oscillations to which the edge
of a continental glacier may have been subject during both its advance
and retreat.
CLASSIFICATION OF STRATIFIED DRIFT ON THE BASIS OF POSITION.
In general the conditions and relations which theoretically should
prevail are those which are actually found.
On the basis of position stratified drift deposits may be classified as
follows:
1. Extraglacial deposits, made by the waters of any glacial epoch if
they flowed and deposited beyond the farthest limit of the ice.
2. Supermorainic deposits, made chiefly during the final retreat of
the ice from the locality where they occur, but sometimes by
extraglacial streams or lakes of a much later time. Locally too,
stratified deposits of an early stage of a glacial epoch, lying on till,
may have failed to be buried by the subsequent passage of the ice over
them, and so remain at the surface. In origin, supermorainic deposits
were for the most part extraglacial (including marginal), so far as the
ice sheet calling them into existence was concerned. Less commonly they
were subglacial, and failed to be covered, and less commonly still
superglacial.
3. The submorainic (basal) deposits were made chiefly by extraglacial
waters in advance of the first ice which affected the region where they
occur. They were subsequently overridden by the ice and buried by its
deposits. Submorainic deposits, however, may have arisen in other ways.
Subglacial waters may have made deposits of stratified drift on surfaces
which had been covered by ice, but not by till, and such deposits may
have been subsequently buried. The retreat of an ice sheet may have left
rock surfaces free from till covering, on which the marginal waters of
the ice may have made deposits of stratified drift. These may have been
subsequently covered by till during a re-advance of the ice in the same
epoch or in a succeeding one. Still again, the till left by one ice
sheet may have been exposed to erosion to such an extent as to have been
completely worn away before the next ice advance, so that stratified
deposits connected with a second or later advance may have been made on
a driftless surface, and subsequently buried.
4. Intermorainic stratified drift may have originated at the outset in
all the ways in which supermorainic drift may originate. It may have
become intermorainic by being buried in any one of the various ways in
which the stratified drift may become submorainic.
CHANGES IN DRAINAGE EFFECTED BY THE ICE.
_While the Ice Was on._
As the continental ice sheet invaded a region, the valleys were filled
and drainage was thereby seriously disturbed. Different streams were
affected in different ways. Where the entire basin of a stream was
covered by ice, the streams of that basin were, for the time being,
obliterated. Where the valley of a stream was partially filled with ice,
the valley depression was only partially obliterated, and the remaining
portion became the scene of various activities. Where the ice covered
the lower course of a stream but not the upper, the ice blocked the
drainage, giving rise to a lake. Where the ice covered the upper course
of a stream, but not its lower, the lower portion was flooded, and
though the river held its position, it assumed a new phase of activity.
Streams issuing from the ice usually carry great quantities of gravel
and sand, and make deposits along their lower courses. Long continued
glacial drainage usually results in a large measure of aggradation. This
was true of the streams of the glacial period.
Where a stream flowed parallel or approximately parallel to the edge of
the advancing ice it was sometimes shifted in the direction in which the
ice was moving, keeping parallel to the front of the ice. All of these
classes of changes took place in this region.
_Wisconsin lake._--Reference has already been made to certain lakes
which existed in the region when the ice was there. The largest of these
lakes was that which resulted from the blocking of the Wisconsin river.
The ice crossed its present course at Kilbourn City, and its edge lay to
the west of the river from that point to Prairie du Sac (see Plate I).
The waters from the area now draining into the Wisconsin must either
have found an avenue of escape beneath the ice, or have accumulated in a
lake west of the edge of the ice. There is reason to believe that the
latter was what happened, and that a great lake covered much of the low
land west of the Wisconsin river above and below Kilbourn City. The
extensive gravel beds on the north flank of the quartzite bluff at
Necedah, and the water-worn pebbles of local origin on the slope of
Petenwell peak (Plate XXXII), as well as the gravels at other points,
are presumably the work of that lake. The waters in this lake, as in
that in the Baraboo valley, probably rose until the lowest point in the
rim of the basin was reached, and there they had their outlet. The
position of this outlet has not been definitely determined, but it has
been thought to be over the divide of the Black river.[8] It is
possible, so far as now known, that this lake was connected with that of
the Baraboo valley. Until topographic maps of this region are made, the
connections will not be easily determined.
[8] Chamberlin: Geology of Wisconsin, Vol. 1.
Even after the ice had retreated past the Wisconsin, opening up the
present line of drainage, the lakes did not disappear at once, for the
ice had left considerable deposits of drift in the Wisconsin valley.
Thus at F, Plates II and XXXVII, and perhaps at other points, the
Wisconsin has made cuts of considerable depth in the drift. Were these
cuts filled, as they must have been when the ice melted, the drainage
would be ponded, the waters standing at the level of the dam. This drift
obstruction at F would therefore have prolonged the history of the lake
which had come into existence when the ice blocked the drainage of the
Wisconsin. As the drift of the valley was removed the level of the lake
sank and finally disappeared.
_Baraboo lake._--Another lake which existed in this region when the ice
was here, occupied the valley of the Baraboo and its tributaries when
the ice blocked the valley at Baraboo. This lake occupied not only the
valley of the Baraboo, but extended up the lower course of every
tributary, presumably rising until it found the lowest point in the rim
of the drainage basin. The location of this point, and therefore the
height of the lake when at its maximum, are not certainly known, though
meager data on this point have been collected. At a point three miles
southeast of Ablemans on the surface of a sandstone slope, water-worn
gravel occurs, the pebbles of which were derived from the local rock. On
the slope below the gravel, the surface is covered with loam which has a
suggestion of stratification, while above it, the soil and subsoil
appear to be the product of local rock decomposition. This water-worn
gravel of local origin on a steep slope facing the valley, probably
represents the work of the waves of this lake, perhaps when it stood at
its maximum height. This gravel is about 125 feet (aneroid measurement)
above the Baraboo river to the north.
Further evidence of a shore line has been found at the point marked T,
Plate II. At this place water-worn gravel of the local rock occurs in
much the same relationship as that already mentioned, and at the same
elevation above the Baraboo river. At a point two and one-half miles
southwest of Ablemans there is local water-worn gravel, with which is
mingled glacial material (pieces of porphyry and diabase) which could
have reached this point only by being carried thither by floating ice
from the glacier. The level of this mixed local and glacial material is
(according to aneroid measurement) approximately the same as that of the
other localities.
When the ice melted, an outlet was opened _via_ the Lower narrows, and
the water of the lake drained off to the Wisconsin by this route. Had
the ice left no drift, the lake would have been promptly drained when
the ice melted; but the lake did not entirely disappear immediately
after the ice retreated, for the drift which the ice left obstructed
drainage to the east. The moraine, however, was not so high as the
outlet of the lake while the ice was on, so that, as the ice retreated,
the water flowed over the moraine to the east, and drew down the level
of the lake to the level of the lowest point in the moraine. The
postglacial cut through the moraine is about ninety feet deep.
Besides being obstructed where crossed by the terminal moraine, the
valley of the Baraboo was clogged to a less extent by drift deposits
between the moraine and the Lower narrows. At one or two places near the
City of Baraboo, such obstructions, now removed, appear to have existed.
Just above the Lower narrows (c, Plate XXXVII) there is positive
evidence that the valley was choked with drift. Here in subsequent time,
the river has cut through the drift-filling of the preglacial valley,
developing a passage about twenty rods wide and thirty-five feet deep.
If this passage were filled with drift, reproducing the surface left by
the ice, the broad valley above it would be flooded, producing a shallow
lake.
The retreat of the ice therefore left two well defined drift dams in the
valley, one low one just above the Lower narrows, and a higher one, the
moraine dam, just west of Baraboo. Disregarding the influence of the
ice, and considering the Baraboo valley only, these two dams would have
given rise to two lakes, the upper one behind the higher dam being
deeper and broader, and covering a much larger area; the lower one
behind the lower dam, being both small and shallow.
Up to the time that the ice retreated past the Lower narrows, the waters
of the upper and lower lakes were united, held up to a common level by
the ice which blocked this pass. After the ice retreated past the Lower
narrows, the level of the Baraboo lake did not sink promptly, for not
until the ice had retreated past the site of the Wisconsin was the
present drainage established. Meantime the waters of the Baraboo lake
joined those of Wisconsin lake through the Lower narrows. If
the lakes had been before connected at some point farther west, this
connection through the narrows would not have changed the level of
either. If they were not before connected, and if the Wisconsin lake was
lower than the Baraboo, this connection would have drawn down the level
of the latter.
Since the drainage from the Baraboo went to the Wisconsin, the Baraboo
lake was not at first lowered below the level of the highest obstruction
in the valley of the Wisconsin even after the ice had retreated beyond
that stream. As the drift obstructions of the Wisconsin valley were
lowered, the levels of all the lakes above were correspondingly brought
down. When the level of the waters in these lakes was brought down to
the level of the moraine dam above Baraboo, the one Baraboo lake of
earlier times became two. The level of the upper of these two lakes was
determined by the moraine above Baraboo, that of the lower by the
highest obstruction below the moraine in either the Baraboo or Wisconsin
valley. The drift obstructions in the Baraboo valley were probably
removed about as fast as those in the Wisconsin, and since the
obstructions were of drift, and the streams strong, the removal of the
dams was probably rapid. Both the upper and lower Baraboo lakes, as well
as the Wisconsin, had probably been reduced to small proportions, if not
been completely drained, before the glacial period was at an end.
_Devil's lake in glacial times._--While the ice edge was stationary in
its position of maximum advance, its position on the north side of the
main quartzite range was just north of Devil's lake (Plate XXXVII). The
high ridge of drift a few rods north of the shore is a well defined
moraine, and is here more clearly marked than farther east or west,
because it stands between lower lands on either side, instead of being
banked against the quartzite ridge. North of the lake it rises about 75
feet above the water. When the ice edge lay in this position on the
north side of the range, its front between the East bluff and the
Devil's nose lay a half mile or so from the south end of the lake. In
this position also there is a well defined moraine.
While the ice was at its maximum stand, it rose above these moraine
ridges at either end of the lake. Between the ice at these two points
there was then a notable basin, comparable to that of the present lake
except that the barriers to the north and southeast were higher than
now. The melting of the ice supplied abundant water, and the lake rose
above its present level. The height which it attained is not known, but
it is known to have risen at least 90 feet above its present level. This
is indicated by the presence of a few drift bowlders on the West bluff
of the lake at this height. They represent the work of a berg or bergs
which at some stage floated out into the lake with bowlders attached.
Bowlders dropped by bergs might be dropped at any level lower than the
highest stand of the lake.
_Other lakes._--Another glacial lake on the East quartzite bluff has
already been referred to. Like the Devil's lake in glacial
time, its basin was an enclosure between the ice on the one hand, and
the quartzite ridge on the other. The location of this lake is shown on
Plate XXXVII (s). Here the edge of the ice, as shown by the position
of the moraine, was affected by a re-entrant curve, the two ends of
which rested against the quartzite ridge. Between the ice on the one
hand and the quartzite ridge on the other, a small lake was formed. Its
position is marked by a notable flat.
With the exception of the north side, and a narrow opening at the
northwest corner, the flat is surrounded by high lands. When the ice
occupied the region, its edge held the position shown by the line
marking the limit of its advance, and constituted an ice barrier to the
north.[9] The area of the flat was, therefore, almost shut in, the only
outlet being a narrow one at t, Plate XXXVII. If the filling of
stratified drift which underlies the flat were removed, the bottom of
the area would be much lower than at present, and much lower than the
outlet at t. It is therefore evident that when the ice had taken its
position along the north side of the flat, an enclosed basin must have
existed, properly situated for receiving and holding water. Since this
lake had but a short life and became extinct before the ice retreated,
its history is here given.
[9] The moraine line on the map represents the crest of the
marginal ridge rather than its outer limit, which is slightly
nearer the lake margin. Stratified drift of the nature of
overwash also intervenes at points between the moraine and
the lake border.
At first the lake had no outlet and the water rose to the level of the
lowest point (t) in the rim of the basin, and thence overflowed to the
west. Meanwhile the sediments borne in by the glacial drainage were
being deposited in the lake in the form of a subaqueous overwash plain,
the coarser parts being left near the shore, while the finer were
carried further out. Continued drainage from the ice continued to bring
sediment into the lake, and the subaqueous overwash plain extended its
delta-like front farther and farther into the lake, until its basin was
completely filled. With the filling of the basin the lake became
extinct. The later drainage from the ice followed the line of the
outlet, the level of which corresponds with the level of the filled lake
basin. This little extinct lake is of interest as an example of a
glacial lake which became extinct by having its basin filled during
glacial times, by sediments washed out from the ice.
Near the northwest corner of this flat, an exposure in the sediments of
the old lake bed shows the curiously contorted layers of sand, silt, and
clay represented in Plate XXXVIII. The layers shown in the
figure are but a few feet below the level of the flat which marks the
site of the lake. It will be seen that the contorted layers are between
two series of horizontal ones. The material throughout the section is
made up of fine-grained sands and clays, well assorted. That these
particular layers should have been so much disturbed, while those below
and above remained horizontal, is strange enough. The grounding of an
iceberg on the surface before the overlying layers were deposited, the
action of lake ice, or the effect of expansion and contraction due to
freezing and thawing, may have been responsible for the singular
phenomenon. Contorted laminae are rather characteristic of the deposits
of stratified drift.
_After the Ice Had Disappeared._
As has already been indicated, the irregular deposition of
glacial drift gave rise to many depressions without outlets in which
surface waters collected after the ice had disappeared, forming ponds or
lakes. So abundant are lakes and ponds and marshes in recently glaciated
regions and so rare elsewhere, that they constitute one of the more
easily recognized characteristics of a glaciated region.
After the ice had melted, the mantle of drift which it left was
sometimes so disposed as to completely obliterate preglacial valleys.
More commonly it filled preglacial valleys at certain points only. In
still other cases a valley was not filled completely at any point,
though partially at many. In this last case, the partial fillings at
various points constituted dams above which drainage was ponded, making
lakes. If the dams were not high enough to throw the drainage out of the
valley, the lakes would have their outlets over them. The drift dam
being unconsolidated would be quickly cut down by the outflowing water,
and the lake level lowered. When the dam was removed or cut to its base,
the lake disappeared and drainage followed its preglacial course.
In case the valley was completely filled, or completely filled at
points, the case was very different. The drainage on the drift surface
was established with reference to the topography which obtained when the
ice departed, and not with reference to the preglacial valleys. Wherever
the preglacial valleys were completely filled, the postglacial drainage
followed lines which were altogether independent of them. When
preglacial valleys were filled by the drift in spots only, the
postglacial streams followed them where they were not filled, only to
leave them where the blocking occurred. In the former case the present
drainage is through valleys which are preglacial in some places, and
postglacial in others.
Thus the drainage changes effected by the drift after the ice was gone,
concerned both lakes and rivers. In this region there are several
illustrations of these changes.
_Lakes._--The lake basins of drift-covered regions are of various types.
Some of them are altogether in drift, some partly in drift and partly in
rock, and some wholly in rock. Basins in the drift were likely to be
developed whenever heavy deposits surrounded thin ones. They are
especially common in the depressions of terminal moraines.
Another class of lake basins occurs in valleys, the basins being partly
rock and partly drift. If a thick deposit of drift be made at one point
in a valley, while above there is little or none, the thick deposit will
form a dam, above which waters may accumulate, forming a pond or lake.
Again, a ridge of drift may be deposited in the form of a curve with its
ends against a rock-ridge, thus giving rise to a basin.
In the course of time, the lakes and ponds in the depressions made or
occasioned by the drift will be destroyed by drainage. Remembering how
valleys develop it is readily understood that the heads of the
valleys will sooner or later find the lakes, and drain them if their
bottoms be not too low.
Drainage is hostile to lakes in another way. Every stream which flows
into a lake brings in more or less sediment. In the standing water this
sediment is deposited, thus tending to fill the lake basin. Both by
filling their basins and by lowering their outlets, rivers tend to the
destruction of lakes, and given time enough, they will accomplish this
result. In view of this double hostility of streams, it is not too much
to say that "rivers are the mortal enemies of lakes."
The destruction of lakes by streams is commonly a gradual process, and
so it comes about that the abundance and the condition of the undrained
areas in a drift-covered region is in some sense an index of the length
of time, reckoned in terms of erosion, which has elapsed since the drift
was deposited.
In this region there were few lakes which lasted long after the ice
disappeared. The basins of the Baraboo and Wisconsin lakes were
partly of ice, and so soon as the ice disappeared, the basins were so
nearly destroyed, and the drift dams that remained so easily eroded,
that the lakes had but a brief history,--a history that was glacial,
rather than postglacial.
The history of the little lake on the East quartzite bluff as
already pointed out, came to an end while the ice was still present.
The beds of at least two other extinct ponds or small lakes above the
level of the Baraboo are known. These are at v and w, Plate XXXVII.
They owed their origin to depressions in the drift, but the outflowing
waters have lowered their outlets sufficiently to bring them to the
condition of marshes. Both were small in area and neither was deep.
_Existing lakes._--Relatively few lakes now remain in this immediate
region, though they are common in most of the country covered by the ice
sheet which overspread this region. Devil's lake only is well known. The
lake which stood in this position while the ice was on, has already been
referred to. After the ice had melted away, the drift which it
had deposited still left an enclosure suitable for holding water. The
history of this basin calls for special mention.
At the north end of the lake, and again in the capacious valley leading
east from its south end, there are massive terminal moraines. Followed
southward, this valley though blocked by the moraine a half mile below
the lake, leads off towards the Wisconsin river, and is probably the
course of a large preglacial stream. Beyond the moraine, this valley is
occupied by a small tributary to the Wisconsin which heads at the
moraine. To the north of the lake, the head of a tributary of the
Baraboo comes within eighty rods of the lake, but again the terminal
moraine intervenes. From data derived from wells it is known that the
drift both at the north and south ends of the lake extends many feet
below the level of its water, and at the north end, the base of the
drift is known to be at least fifty feet below the level of the bottom
of the lake. The draining of Devil's lake to the Baraboo river is
therefore prevented only by the drift dam at its northern end. It is
nearly certain also, that, were the moraine dam at the south end of the
lake removed, all the water would flow out to the Wisconsin, though the
data for the demonstration of this conclusion are not to be had, as
already stated.
There can be no doubt that the gorge between the East and West bluffs
was originally the work of a pre-Cambrian stream, though the depth of
the pre-Cambrian valley may not have been so great as that of the
present. Later, the valley, so far as then excavated, was filled with
the Cambrian (Potsdam) sandstone, and re-excavated in post-Cambrian and
preglacial time. Devil's lake then occupies an unfilled portion of an
old river valley, isolated by great morainic dams from its surface
continuations on either hand. Between the dams, water has accumulated
and formed the lake.
_Changes in Streams._
In almost every region covered by the ice, the streams which established
themselves after its departure follow more or less anomalous courses.
This region is no exception. Illustrations of changes which the
deposition of the drift effected have already been given in one
connection or another in this report.
_Skillett creek._--An illustration of the sort of change which drift
effects is furnished by Skillett creek, a small stream tributary to the
Baraboo, southwest of the city of that name. For some distance from its
head (a to b, Fig. 43) its course is through a capacious preglacial
valley. The lower part of this valley was filled with the water-laid
drift of the overwash plain. On reaching the overwash plain the creek
therefore shifted its course so as to follow the border of that plain,
and along this route, irrespective of material, it has cut a new channel
to the Baraboo. The postglacial portion of the valley (b to c) is
everywhere narrow, and especially so where cut in sandstone.
The course and relations of this stream suggest the following
explanation: Before the ice came into the region, Skillett creek
probably flowed in a general northeasterly direction to the Baraboo,
through a valley comparable in size to the preglacial part of the
present valley. As the ice advanced, the lower part of this valley was
occupied by it, and the creek was compelled to seek a new course. The
only course open to it was to the north, just west of the advancing ice,
and, shifting westward as fast as the ice advanced, it abandoned
altogether its former lower course. Drainage from the ice then carried
out and deposited beyond the same, great quantities of gravel and sand,
making the overwash plain. This forced the stream still farther west,
until it finally reached its present position across a sandstone ridge
or plain, much higher than its former course. Into this sandstone it has
since cut a notable gorge, a good illustration of a postglacial valley.
The series of changes shown by this creek is illustrative of the changes
undergone by streams in similar situations and relations all along the
margin of the ice.
[Illustration: Fig. 43.--Skillett Creek, illustrating the points
mentioned in the text.]
The picturesque glens (Parfrey's and Dorward's) on the south face of the
East bluff are the work of post-glacial streams. The preglacial valleys
of this slope were obliterated by being filled during the glacial epoch.
_The Wisconsin._--The preglacial course of the Wisconsin river is not
known in detail, but it was certainly different from the course which
the stream now follows. On Plate I the relations of the present stream
to the moraine (and former ice-front) may be seen.[10] As the ice
approached it from the east, the preglacial valley within the area here
under consideration was affected first by the overwash from the moraine,
and later by the ice itself, from the latitude of Kilbourn City to
Prairie du Sac.
[10] The preglacial course was probably east of the present
in the vicinity of Kilbourn City.
It has already been stated that the ice probably dammed the river, and
that a lake was formed above Kilbourn City, reaching east to the ice and
west over the lowland tributary to the river, the water rising till it
found an outlet, perhaps down to the Black river valley.
When the ice retreated, the old valley had been partly filled, and the
lowest line of drainage did not everywhere correspond with it. Where the
stream follows its old course, it flows through a wide capacious valley,
but where it was displaced, it found a new course on the broad flat
which bordered its preglacial course. Displacement of the stream
occurred in the vicinity of Kilbourn City, and, forced to find a new
line of flow west of its former course, the stream has cut a new channel
in the sandstone. To this displacement of the river, and its subsequent
cutting, we are indebted for the far-famed Dalles of the Wisconsin.
But not all the present route of the river through the dalles has
been followed throughout the entire postglacial history of the stream.
In Fig. 44, the depression A, B, C, was formerly the course of the
stream. The present course between D and E is therefore the youngest
portion of the valley, and from its lesser width is known as the
"narrows." During high water in the spring, the river still sends part
of its waters southward by the older and longer route.
The preglacial course of the Wisconsin south of the dalles has never
been determined with certainty, but rational conjectures as to its
position have been made.
The great gap in the main quartzite range, a part of which is occupied
by Devil's lake, was a narrows in a preglacial valley. The only streams
in the region sufficiently large to be thought of as competent to
produce such a gorge are the Baraboo and the Wisconsin. If the Baraboo
was the stream which flowed through this gorge in preglacial time, the
comparable narrows in the north quartzite range--the Lower narrows of
the Baraboo--is to be accounted for. The stream which occupied one of
these gorges probably occupied the other, for they are in every way
comparable except in that one has been modified by glacial action, while
the other has not.
[Illustration: Fig. 44.--The Wisconsin valley near Kilbourn City.]
The Baraboo river flows through a gorge--the Upper narrows--in the north
quartzite range at Ablemans, nine miles west of Baraboo. This gorge is
much narrower than either the Lower narrows or the Devil's lake gorge,
suggesting the work of a lesser stream. It seems on the whole
probable, as suggested by Irving,[11] that in preglacial time the
Wisconsin river flowed south through what is now the Lower narrows of
the Baraboo, thence through the Devil's lake gorge to its present valley
to the south. If this be true, the Baraboo must at that time have joined
this larger stream at some point east of the city of the same name.
[11] Irving. Geology of Wisconsin, Vol. II.
_The Driftless Area._
Reference has already been made to the fact that the western part of the
area here described is driftless, and the line marking the limit of ice
advance has been defined. Beyond this line, gravel and sand, carried
beyond the ice by water, extends some distance to the west. But a large
area in the southwestern part of the state is essentially free from
drift, though it is crossed by two belts of valley drift (valley trains)
along the Wisconsin and Mississippi rivers.
The "driftless area" includes, besides the southwestern portion of
Wisconsin, the adjoining corners of Minnesota, Iowa and Illinois. In the
earlier epochs of the glacial period this area was completely surrounded
by the ice, but in the last or Wisconsin epoch it was not surrounded,
since the lobes did not come together south of it as in earlier times.
(Compare Plate XXXIII and Fig. 36.)
Various suggestions have been made in the attempt to explain the
driftless area. The following is perhaps the most satisfactory:[12]
[12] Chamberlin and Irving. Geology of Wisconsin, Vols. I and
II.
The adjacent highlands of the upper peninsula of Michigan, are bordered
on the north by the capacious valley of Lake Superior leading off to the
west, while to the east lies the valley of Lake Michigan leading to the
south. These lake valleys were presumably not so broad and deep in
preglacial times as now, though perhaps even then considerable valleys.
When the ice sheet, moving in a general southward direction from the
Canadian territory, reached these valleys, they led off two great
tongues or lobes of ice, the one to the south through the Lake Michigan
depression, the other to the south of west through the Lake Superior
trough. (Fig. 36.) The highland between the lake valleys conspired with
the valleys to the same end. It acted as a wedge, diverting the ice to
either side. It offered such resistance to the ice, that the thin and
relatively feeble sheet which succeeded in surmounting it, did not
advance far to the south before it was exhausted. On the other hand, the
ice following the valleys of Lakes Superior and Michigan respectively,
failed to come together south of the highland until the latitude of
northern Iowa and Illinois was reached. The driftless area therefore
lies south of the highlands, beyond the limit of the ice which
surmounted it, and between the Superior and Michigan glacial lobes above
their point of union. The great depressions, together with the
intervening highland, are therefore believed to be responsible for the
absence of glaciation in the driftless area.
_Contrast Between Glaciated and Unglaciated Areas._
The glaciated and unglaciated areas differ notably in (1) topography, (2)
drainage, and (3) mantle rock.
1. _Topography._--The driftless area has long been exposed to the
processes of degradation. It has been cut into valleys and ridges by
streams, and the ridges have been dissected into hills. The
characteristic features of a topography fashioned by running water are
such as to mark it clearly from surfaces fashioned by other agencies.
Rivers end at the sea (or in lakes). Generally speaking, every point at
the bottom of a river valley is higher than any other point in the
bottom of the same valley nearer the sea, and lower than any other point
correspondingly situated farther from the sea. This follows from the
fact that rivers make their own valleys for the most part, and a river's
course is necessarily downward. In a region of erosion topography
therefore, tributary valleys lead down to their mains, secondary
tributaries lead down to the first, and so on; or, to state the same
thing in reverse order, in every region where the surface configuration
has been determined by rain and river erosion, every gully and every
ravine descends to a valley. The smaller valleys descend to larger and
lower ones, which in turn lead to those still larger and lower. The
lowest valley of a system ends at the sea, so that the valley which
joins the sea is the last member of the series of erosion channels of
which the ravines and gullies are the first. It will thus be seen that
all depressions in the surface, worn by rivers, lead to lower ones. The
surface of a region sculptured by rivers is therefore marked by valleys,
with intervening ridges and hills, the slopes of which descend to them.
All topographic features are here determined by the water courses.
[Illustration: Fig. 45.--Drainage in the driftless area. The absence of
ponds and marshes is to be noted.]
The relief features of the glaciated area, on the other hand, lack the
systematic arrangement of those of the unglaciated territory, and stream
valleys are not the controlling elements in the topography.
2. _Drainage._--The surface of the driftless area is well drained. Ponds
and lakes are essentially absent, except where streams have been
obstructed by human agency. The drainage of the drift-covered area, on
the other hand, is usually imperfect. Marshes, ponds and lakes are of
common occurrence. These types are shown by the accompanying maps, Figs.
45 and 46, the one from the driftless area, the other from the
drift-covered.
[Illustration: Fig. 46.--Drainage in a glaciated region. Walworth and
Waukesha counties, Wisconsin, showing abundance of marshes and lakes.]
3. _Mantle rock._--The unglaciated surface is overspread to an average
depth of several feet by a mantle of soil and earth which has resulted
from the decomposition of the underlying rock. This earthy material
sometimes contains fragments and even large masses of rock like that
beneath. These fragments and masses escaped disintegration because of
their greater resistance while the surrounding rock was destroyed. This
mantle rock grades from fine material at the surface down through
coarser, until the solid rock is reached, the upper surface of the rock
being often ill-defined (Fig. 47). The thickness of the mantle is
approximately constant in like topographic situations where the
underlying rock is uniform.
The residual soils are made up chiefly of the insoluble parts of the
rock from which they are derived, the soluble parts having been removed
in the process of disintegration.
[Illustration: Fig. 47.--Section in a driftless area, showing relation
of the mantle rock to the solid rock beneath.]
With these residuary soils of the driftless area, the mantle rock of
glaciated tracts is in sharp contrast. Here, as already pointed out, the
material is diverse, having come from various formations and from widely
separated sources. It contains the soluble as well as the insoluble
parts of the rock from which it was derived. In it there is no
suggestion of uniformity in thickness, no regular gradation from fine to
coarse from the surface downward. The average thickness of the drift is
also much greater than that of the residual earths. Further, the contact
between the drift and the underlying rock surface is usually a definite
surface. (Compare Figs. 32 and 47.)
POSTGLACIAL CHANGES.
Since the ice melted from the region, the changes in its geography have
been slight. Small lakes and ponds have been drained, the streams whose
valleys had been partly filled, have been re-excavating them, and
erosion has been going on at all points in the slow way in which it
normally proceeds. The most striking example of postglacial erosion is
the dalles of the Wisconsin, and even this is but a small gorge for so
large a stream. The slight amount of erosion which has been accomplished
since the drift was deposited, indicates that the last retreat of the
ice, measured in terms of geology and geography, was very recent. It has
been estimated at 7,000 to 10,000 years, though too great confidence is
not to be placed in this, or any other numerical estimate of
post-glacial time.
INDEX.
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PAGES
Ablemans 66,67
Baraboo Lake 130
Baraboo Quartzite ranges 2, 65
Constitution of 14
Dynamic action in 15, 17, 18
Gaps in--
Devil's Lake Gap 3, 13
Lower Narrows 5, 13, 67
Narrows Creek 66
Upper Narrows 5, 10, 17, 19, 67
Igneous rock in 18
Structure of 15
Topography of 5, 13
Base-level 47
Base-level plains 50
Bowlder clay 97
Breccia 18
Castle Rock 71
Cleopatra's Needle 65
Cold Water Canyon 70
Conglomerate 10, 28
Basal (Potsdam) 29
Corrasion 36
Cross-bedding 30
Cycle of erosion 44, 47
Dalles of the Wisconsin 69
Origin of 53
Scenery of 69, 140
Dell Creek 53
Deltas 30, 56, 120
Deposits--
By extra-glacial waters 115-123
By ice 85, 94
By rivers 55, 56
By subglacial streams 124
Of drift classified 127
Devil's Doorway 65
Devil's Lake 132
History of 132
In glacial times 132
Location 3, 9
Origin of 132
Devil's Nose 5, 110
Divides, Shifting of 44
Dorward's Glen 10, 14, 29, 68
Drift 73
Characteristics of 96
Constitution of 94
Deposits classified 127
Effect on topography 85, 88
Relation of stratified to unstratified 125
Stratified 111
Topography of 101, 103
Driftless area 79, 142
Drainage--
Adjustment of 62
Changes in, effected by the ice 128, 142
Establishment of 61
Glacial 113
Of drift-covered area 144
Of driftless area 144
Postglacial changes in 146
Endmoraene 108
Erosion--
By rain, and rivers, general outline of 36-58
Elements of 36
Of folded strata 50
Of rocks of unequal hardness 47
Of the quartzite 25
Preglacial 60
Topography 12
Without valleys 37
Eskers 124
Falls 48
Fossils--
In limestone 12
In sandstone 9, 11
Friendship mounds 71
Geographic features, general 3-20
Glacial drainage 113
Glaciated area 78, 91, 143
Glacier ice--
Deposition by 85
Direction of movement 88
Erosive work of 79-84
Formation of 74
Movement of, affected by topography 89
Glens 68
Green Bay lobe 91
Gibraltar rock 63
Ground Moraine--
Constitution of 99
Location of 97
Topography of 101
Groundwater level 41
Ice sheets--
Formation of 74
History of 114
Movement of 75, 88
North American ice sheet 78
Igneous rock 18
Intermittent streams 42
Kames 115
Lakes--
Wisconsin Lake 129
Baraboo Lake 130
Devil's Lake 3, 9, 132, 137
Limestone, see Lower Magnesian.
Lower Magnesian limestone--
Fossils of 12
History of 31-32
Occurrence of 11
Origin of 11
Position of 12
Structure of 8
Lower Narrows 5, 13, 67
Mantle rock 20, 144
Metamorphism 14, 24
Monadnocks 51
Moraines (see terminal moraine and ground moraine).
Morainic aprons 119
Narrows 49
In quartzite 66, 67
Natural bridge 69
Navy Yard 69
Niagara limestone 33
North American ice sheet 78
Nunatak 89
Osars (see Eskers).
Outwash plains 118, 120
Overwash plains 118, 120
Parfrey's Glen 10, 14, 29, 68
Peneplain 47, 50
Pewit's nest 9, 53, 69
Pine Hollow 69
Postglacial changes 146
Potsdam sandstone--
Fossils of 9, 11
History of 27-31
Origin of 9-11
Relation to quartzite 19
Structure of 8
Quartzite (see also Baraboo quartzite ranges)--
Dynamic Metamorphism of 24
Erosion of 25
Origin of 23
Submergence of 27
Thickness of 26
Uplift of 24
Rapids 48
Rejuvenation of streams 56
Ripple marks 9, 15
Roches moutonnee 81
Sandstone (see Potsdam and St. Peters).
Sauk Prarie 117, 118, 119
Skillett Creek 8, 53, 138
Slope of upper surface of ice 111
Snow fields 74
Soil 7, 144, 146
Stand rock 70
Steamboat rock 70
St. Peter's sandstone 32
Stratified drift 111-112, 125
Streams, changes in 138
Subaqueous overwash plains 120
Subglacial till (ground moraines) 99
Sugar Bowl 70
Talus slopes 65
Terminal moraines--
Across the United States 78
Development of 102
In Devil's Lake region 105
Boundaries of 106
Location of 92, 93, 108
On the main quartzite range 107
Width of 106
Topography of 103
Till 97
Topography--
Effect of, on ice movement 89
Erosion topography 12
Of drift-covered country 8, 143
Of driftless area 6, 7, 12, 143
Of plain surrounding quartzite ridge 6
Of quartzite ridges 5
Transportation by streams 55
Tributary valleys 39
Turk's Head 65
Unconformity 19
Underground water 58
Unglaciated areas 79, 142, 143
Unstratified drift 99, 102, 125
Upper Narrows 5, 10, 17, 19, 67
Valley, the--
Beginning of 37
Characteristics of, at various stages 52-54
Course of 39
How a valley gets a stream 40
Limits of 43
Valley trains 116
Waterfalls 48
Weathering 36
Webster's Prarie 119
Wisconsin Lake 129
Wisconsin River 139
Witch's Gulch 70