connection with the history of an inland region is the determination of
changes of level. By leveling along an ancient beach, post-lacustral
changes in the relative elevations of various points may be readily
ascertained. Pre-lacustral changes, however, by which ancient valleys
have been obstructed, are much more difficult of direct observation,
but might appear from the study of the hard-rock topography, as has
already been suggested. This branch of the investigation, however,
should more properly begin at the coast and be extended inland.
8. _Former outlets._ Several localities where the waters of the
Laurentian basin have overflowed during former high-water stages have
been pointed out, but some confusion has arisen in this connection,
for the reason that the channels formed by streams issuing from the
margin of the ice during the closing stages of the Glacial epoch have,
in some instances, been mistaken for evidence of former lake outlets.
The old outlets which seem to have been well determined are situated at
different levels, and show that the entire basin could not have been
occupied by a single great water-body, unless, as has been supposed
by some, it was in direct communication with the sea. This hypothesis
will be considered below. It has sometimes been assumed that all of the
basin below the level of some ancient outlet was once flooded, so as to
form a great lake in all of the basin now situated at a lower level;
but, in making such generalizations, the possibility of places in the
rim of the basin being at a lower level than the outlet discovered,
thus necessitating a special explanation, such as the partial
occupation of the basin by glacial ice, or changes in elevation of such
a character as to raise the locality of former overflow or to depress
other regions, have to be considered.
Former outlets should bear a definite relation to neighboring shore
lines and to sedimentary deposits. The channels leading from former
points of discharge merit examination, as here again changes of level
may perhaps be detected in the gradients of stream terraces.
Most of the ancient outlets thus far recognized lead southward, but
as previously mentioned, a former channel of discharge north of Lake
Superior has recently been reported. If this observation is confirmed,
it will have an important bearing on questions relating to changes of
level and to the position of the ice front during the later stages in
the retreat of the glaciers.
9. _Probable effects of a retreating ice sheet on drainage._ The
generally accepted conclusion that glaciers advanced southward and
occupied the Laurentian basin during the Glacial epoch and retreated
northward toward the close of that epoch, is sustained by a vast body
of evidence. As the ice sheet withdrew it left a superficial deposit
frequently one or two hundred feet thick over nearly all of the region
it abandoned, and pre-glacial drainage lines were obstructed and mostly
obliterated. As long as the slope in front of the ice was southward,
the drainage from it found ready means of escape, but when the slope
was northward towards the ice front, the drainage was obstructed and
lakes were formed.
We have good reasons for believing that the topography of the
Laurentian region was essentially the same at the close of the Glacial
epoch as it is now, but the broader question of continental elevation
is less definite. The inequalities of the surface being essentially as
we now find them, it would follow that the first lake formed when the
ice retreated to the north of the divide running through central Ohio
and central New York, would be small and dependent on minor features
in the relief of the land, and would discharge southward. As the ice
retreated, the lakes would expand and become united one with another
and the larger lakes thus formed would still find outlet across the
southern rim of the basin. As the glaciers continued to retreat lower
and lower, passes would become free of ice and the lakes would be
drained at lower levels, old beaches would be abandoned, the lakes
would contract, and finally separate lakes would be formed in the
lowest depression in the basins of the more ancient water bodies. The
shape of the retreating ice front would be determined by topographic
conditions and would in turn determine the northern outline of the
lakes along its margin. This in brief is one hypothesis that has been
proposed to explain the varied history recorded by the shore records,
sediments, etc., within the basin.
10. _Communication with the sea._ Another hypothesis which assumes
to account for some of the facts observed, is that the continent was
depressed at the close of the Glacial epoch sufficiently to allow the
sea to have access to the Laurentian basin. This hypothesis is coupled
with others which do not recognize a period of Pleistocene glaciation,
but, as already suggested, this is a matter that is considered by the
great body of American geologists as not being any longer open to
profitable discussion.
In the study here outlined the question whether the water bodies which
formerly occupied the Laurentian basin were lakes or arms of the
sea, should not be difficult of direct and positive determination.
If fossils can be found within the basin, they might yield definite
testimony, but even if they are absent or if their evidence is
inconclusive, topography can be appealed to with the expectation of
receiving a conclusive decision.
If the Laurentian basin was occupied by an arm of the sea during
various stages in the Pleistocene elevation, then the records of such
a submergence should occur both within and without the depression,
and direct connection between the two should be expected. If the
waters within the basin were capable of making such well-defined
shore records as are now found, we are justified in assuming that the
true ocean beach on the outer slopes of the basin would be still more
conspicuous. Again, the waters within the basin deposited a sheet of
sediment, certainly not less than one hundred feet thick; to be sure
the conditions for rapid accumulation were there present, but if the
ocean covered the adjacent land it should have left similar deposits.
This is abundantly proven in the St. Lawrence and Champlain valleys,
where clays containing marine fossils occur up to a certain horizon and
record a Pleistocene invasion of these depressions by the sea. If the
adjacent Ontario basin was occupied by the sea about the same time that
the Champlain valley received its filling of clays containing marine
fossils, there is every reason to believe that the deposits and their
contained fossils in each basin would have been essentially the same.
One of the best known of the ancient shore lines about Lake Ontario has
an average elevation of approximately 500 feet above the sea. If the
sea had access to the basin at the time this breech was formed, then at
corresponding horizon without the basin especially, to the south and
southeast, where the full force of the Atlantic’s waves would have been
felt, there should be still more prominent beaches.
Many well-defined shore lines in the Laurentian basin are much higher
than the one just referred to, and if these were also formed during
various stages of submergence, as has been claimed, it is evident that
ocean beaches and ocean sediments of Pleistocene age should be looked
for over nearly the whole of the eastern part of the United States. The
student may easily answer this question for himself, and thus perhaps
make a contribution to the subject here treated.
In the investigation here outlined, the work of previous observers
should not be ignored, and every plausible hypothesis that has been
advanced to account for the facts observed should be carefully tested.
In writing these pages I have not quoted the writing of others, for the
reason that a discussion of evidence has not been the aim in view, and
also because the writings examined are so numerous that justice could
not be done them in the space at command. That the literature relating
to the subject is voluminous is indicated by the fact that an annotated
bibliography of the Pleistocene history of the Laurentian basin, now in
preparation, already contains over 200 entries of individual papers.
ISRAEL C. RUSSELL.
FOOTNOTES
[52] The Topographic Features of Lake Shores, by G. K. Gilbert, in
Fifth Ann. Rep. U. S. Geological Survey 1883–4.
[53] Preliminary Paper on the Terminal Moraine of the Second Glacial
Epoch, by T. C. Chamberlin, in Third Ann. Rep. U. S. Geological
Survey, 1881–2.
_EDITORIALS._
The Summer meeting of the Geological Society of America will be held
at Madison, Wis., on August 15 and 16. The session of the American
Association for the Advancement of Science will begin at the same
place on the 17th of August and extend to the 23d. The Congress of
Geologists, under the auspices of the Columbian Exposition, will begin
at Chicago, on August 24, and continue its sessions so long as its
work may require. Preliminary to this series of meetings, Professors
M. E. Wadsworth and C. R. Van Hise will meet such geologists as care to
visit the Lake Superior region at the Commercial Hotel, Iron Mountain,
Mich., on the forenoon of August 7, and will act as guides during the
week following. A carefully prepared scheme for the trip is announced,
embracing visits to the leading points of interest in the Menominee,
Marquette and Gogebic iron districts, and in the copper-bearing region
of Keweenaw Point. Those who desire to participate in the excursion, or
who wish information regarding it, should address Professor Van Hise,
at Madison.
In connection with the meetings of the Geological Society and the
American Association at Madison, there will be excursions to the
Devil’s Lake region, to the Dells of the Wisconsin, and to the
driftless area, under the guidance of geologists personally familiar
with the features of most special interest. The article of Professor
Van Hise in this number is a timely presentation of some points of
peculiar significance in the first named region, and will prove very
serviceable to those who choose the excursion to that region.
It is proposed to hold the sessions of the Congress at Chicago at the
Art Institute during the forenoons, leaving the afternoons free for
visiting the Exposition. Experience has shown that a half day devoted
to looking at exhibits, where there is such a plethora of objects
of interest as in the Exposition, taxes the faculties of observation
to the full extent of their pleasurable employment. Attendance upon
the Congress and the study of the Exposition will, therefore, it is
thought, constitute agreeable and profitable complements of each other.
Excursions to points of geological interest in the vicinity of Chicago
will be privately arranged, if desired.
These three meetings, with the attending excursions and the study of
the Exposition, constitute a rare combination of opportunities which
will doubtless be embraced very generally by the geologists of the
country.
T. C. C.
*.*
The supply of numbers one and two of this JOURNAL remaining in the
hands of the publishers has become reduced below the limit they desire
to preserve for binding and for special purposes, and they would esteem
it a great favor on the part of those who may have received duplicates,
as sample copies or by the accidents of mailing while the lists were
imperfect, if they would return such duplicates to them. They will
gladly return the postage if the address of the sender is placed on the
wrapper.
_REVIEWS._
CRYSTALLINE ROCKS FROM THE ANDES.
_Untersuchungen an altkrystallinen Schiefergesteinen aus dem Gebiete
der argentinischen Republik_ von B. KÜHN. Neues Jahrbuch für
Min., etc., Beit. Bd. VII., 1891, p. 295.
_Untersuchung argentinischer Pegmatite, etc._, von P. SABERSKY, _ib._
p. 359.
_Untersuchungen an argentinischen Graniten, etc._, von J. ROMBERG,
_ib._, VIII., 1892, p. 275.
Travelers and foreign residents in South America are rapidly furnishing
information relative, not only to the volcanic, but also to the older
crystalline rocks composing the great Andes chain. Since the early
observations of Darwin,[54] the petrographical collections made by
Stelzner during his three years’ residence, as professor, at Cordova
(1873–1876) have been described by himself[55] and Franke,[56] while
the results of detailed studies of the more extensive collections
gathered by Stelzner’s successor, Professor L. Brackebusch, are now
beginning to appear. Professor Brackebusch’s residence in the Argentine
Republic lasted from 1876 till 1883, and during this period he made
numerous scientific expeditions.[57] The petrographical material
thus obtained has been confided to specialists in Germany for study.
Three papers dealing with the crystalline schists (gneisses),[58]
pegmatites,[59] and granites,[60] have recently appeared. The rocks of
the granite contact-zones had been placed in Professor Lessen’s hands
before his death, while communications on other special groups are
doubtless to be expected.
These investigations naturally suffer from the forced absence of
all field observations on the part of their authors, but the purely
petrographical study of the material brings to light many points of
interest, while it furnishes the only sort of detailed information
regarding the rocks of these remote regions which we can for the
present hope for. It is here desired only to direct attention to a few
of the most striking results obtained from the Brackebusch material by
the three authors last cited.
Dr. Kühn’s paper on the crystalline schists treats principally of
gneiss, and offers little that is new. It is mostly occupied with
additional evidence of structural and chemical changes due to dynamic
metamorphism in the sense of Lehmann. The most noteworthy of these are
development and microstructure of fibrolite; production of augen-gneiss
from porphyritic granite; development of microcline structure in
orthoclase by pressure; secondary origin of microcline, microperthite
and micropegmatite; alteration of garnet to biotite and hornblende.
Dr. Sabersky’s paper on the coarse-grained granites or pegmatites is
entirely mineralogical, and is devoted principally to elucidating the
structure of microcline. The author concludes that the well-known
gridiron structure is due, not to two twinning laws (the Albite and
Pericline), as has been generally supposed, but to the Albite law
alone, in accordance with which the individuals form both contact and
penetration twins, like the albite crystals from Roc-tourné, described
by G. Rose.
Dr. Romberg’s paper on the Argentine granites is much more
extensive than the two preceding. It is embellished by seventy-two
microphotographs, many of which admirably illustrate the special
points described. He comes to several results of great petrographical
significance, the most important of which relate to the origin of
quartz-feldspar intergrowths in granitic rocks. He clearly shows that
beside the original granite quartz there is also much of a secondary
nature present. This is not microscopically distinguishable from the
original mineral, but its later genesis is demonstrated by many careful
observations on its relation to other constituents. The abundant
secondary quartz is regarded as the product of weathering--principally
of the feldspar, into which it has a peculiar tendency to penetrate.
The extreme sensitiveness of quartz to pressure is emphasized (as
it has been by Lehmann and the present writer) and illustrated by
undulatory extinction, banding, granulation and even plastic bending
around other minerals. Dynamic action is regarded as the efficient
cause of the secondary impregnation of feldspar by quartz, and a union
of this with weathering of the feldspar as the source of the abundant
and complex pegmatitic intergrowths of quartz and feldspar.
These results are important, and they will now doubtless come to
be generally recognized. It is, however, of interest to observe in
this connection that all which is here announced as new in regard to
secondary and “corrosion” quartz was described and figured in even
greater detail by Prof. R. D. Irving ten years ago. This does not
appear to be known to Dr. Romberg, for he does not allude to it, but
anyone who will turn to pages 99 to 124 and plates XIII, XIV and XV of
the monograph on the Lake Superior Copper Rocks (vol. 5, U. S. Geol.
Survey, Washington, 1883) will find his conclusions stated in almost
the same language and with a much wider range of fact and illustration.
Dynamic action is not here adduced as a cause for the saturation of
feldspar by secondary micropegmatitic quartz, since the Lake Superior
rocks show no evidence of having been subjected to pressure, but
that the quartz itself has been derived from the leaching of the
feldspar substance and that the impregnation is mostly confined to the
orthoclase is clearly stated.
Dr. Romberg also demonstrates, in a number of cases, the secondary
origin of albite, especially as microperthite, and of microcline.
He gives details relating to each of the mineral constituents, and
then the effects of pressure and of chemical action on the most
important of them. Among many interesting observations but a few
can be even mentioned here; such, for instance, as the original
character of muscovite in many granites; the alteration of garnet
into muscovite; the dependence of the well-known pleochroic halos in
biotite and cordierite upon the substance of the zircon which they
almost invariably surround, and secondary rutile needles which grow
out from biotite into both quartz and feldspar. In one rock occurring
in a granite a violet, strongly pleochroic mineral was found, which,
in neither composition nor physical properties, agreed exactly with
any known species. It seems to be intermediate between andalusite
and dumortierite, but, as its individuality is not yet perfectly
established, no new name is proposed for it.
G. H. WILLIAMS.
_The Mineral Industry, its Statistics, Technology and Trade, in the
United States and Other Countries, from the Earliest Times to the
End of 1892._ Vol. I. Edited by RICHARD P. ROTHWELL, editor of
the _Engineering and Mining Journal_. 629 pp., 8vo.
This volume is a statistical supplement of the _Engineering and Mining
Journal_, and is published by the Scientific Publishing Co., of New
York, 1893. It takes the place of the former annual statistical number
of the _Engineering and Mining Journal_, and it is the first volume
of a series which is to be issued annually. The object of the present
volume is to make known, as soon as possible after the expiration
of the year 1892, the statistics and the various conditions of the
mining industry in that year and in previous years. The future volumes
will, each year, bring these statistics up to date, and thus the full
particulars of the mining industry will be known within a few days of
the expiration of every year. The volume is a compilation of articles
written by different authors, and the names of these writers are
guarantee that the different subjects have been treated by authorities
in the departments with which they deal. The editor himself, it is
but justice to him to state, has written some of the most important
parts of the volume, notably the article on the statistics of gold and
silver, and his well-known familiarity with the subjects he discusses
renders the reader confident of their accuracy.
The present volume is not confined to the bare presentation of figures
of production and consumption of various mineral products, but it
treats each individual branch of the mining industry in its various
departments; and in this way the volume really represents a series of
treatises on the various mining products and the methods of treating
them. The production of each material is given not only for the United
States but also for foreign countries; the conditions of the American
and foreign markets during 1892 and previous years are discussed, while
the various uses of the different materials, the history of mining in
different districts, the means of transportation, the metallurgical
methods of treating different ores, the methods of sampling, and the
possibilities of competition in various mining industries are also
described. In addition to this, tables of assessments levied and
dividends paid by various mining companies are given. The volume ends
with a concise statement of the statistics and condition, as well as
the extent, of the mining industries of foreign countries. Thus there
is presented, in a volume of no excessive size, a complete and concise
epitome of the mining industries of the world; and this work was
completed almost immediately after the time to which it relates.
The various subjects are treated in the following order: A résumé and
tables of statistics of the mineral products of the United States;
articles on Aluminum, Antimony, Asbestos, Asphaltum, Barytes, Bauxite,
Borax, Bromine, Cement, Chemical Industry, Chromium, Coal and Coke,
Copper, Corundum and Emery, Cryolite, Feldspar, Fluorspar, Gold and
Silver, Iron and Steel, Lead, Manganese, Mica, Nickel and Cobalt,
Onyx, Petroleum, Phosphate Rock, Platinum Group of Metals, Plumbago,
Precious Stones, Pyrites, Quicksilver, Salt, Soda, Sulphur, Talc,
Tin, Whetstones and Novaculite, Zinc; Tables of Assessments Levied by
Mining Companies from 1887–1893; Tables of Dividends Paid by American
Mining Companies; Baltimore Mining Stock Market, Boston Mining Stock
Market, Denver Mining Stock Market, London Mining Stock Market, Lake
Superior Mining Stock Market, New York Mining Stock Market, Paris
Mining Stock Market, Pittsburg Mining Stock Market, Salt Lake City
Mining Stock Market in 1892, San Francisco Mining Stock Market; Foreign
Countries--Austria-Hungary, Belgium, Canada, China, France, Germany,
Italy, Japan, Russia, South American Countries, Spain and Cuba, Sweden,
United Kingdom of Great Britain and Ireland.
The importance of the subject treated in this volume can be appreciated
when it is known that the products of the mines of the United States
alone in the census year of 1889 amounted to $587,230,662, and that
this amount really only represents the interest on an immensely larger
capital invested. The mining products of the United States are far more
important in their aggregate value than those of any other country in
the world, though, in many individual products, other countries supply
more than the United States. This country is first, however, in the
production of pig iron and steel. It is also first in the production of
copper, gold, silver, petroleum, and a number of other products. Great
Britain is still the leader in the production of coal, but the United
States’ production is rapidly growing and already equals 81.08% of the
British production, and supplies 28.75% of the world’s consumption.