THE STEPPE PERIOD.
The occurrence of a period marked by dry climate over wide areas of
the Eurasian continent, and possibly also in North America, is
evidenced by the widespread distribution of an accumulation known as
_loess_, concerning the origin of which there has been much difference
of opinion, though that it was formed subsequently to the glacial
period seems to be generally admitted, inasmuch as it is largely
composed of rearranged glacial mud. The formation of the loess as a
steppe-deposit was first advocated by Baron von Richthofen, and his
views were supported by Nehring after study of the loess-fauna.
Richthofen's explanation of the loess as due to the spread of dust by
wind in a dry region is becoming widely accepted, and it necessitates
the widespread occurrence of steppe conditions, as the loess has a
very extensive geographical range, and may be truly regarded as the
normal continental deposit of Eurasia during the period immediately
succeeding the glacial period. In our own country, as the sea cannot
have been far distant during these times the normal loess is not
found, but several accumulations occur, which on stratigraphical and
palæontological grounds must be regarded as synchronous with the
formation of the loess. These are certain rubble-drifts of the
southern counties, the older river-gravels of southern England, and
some of the older cave deposits of various parts of England. It is
doubtful whether any classification into minute subdivisions can be
adopted for them, though Prof. Boyd Dawkins has advocated their
separation into an older age of River Drift Man, and a newer period of
Cave Man, on account of the evidences of a lower state of civilisation
afforded by examination of the River Drift implements when compared
with those fashioned by Cave Man. Roughly speaking, the Steppe period
corresponds with the period during which Palæolithic man existed, at
any rate in north-west Europe, and we may speak of the Steppe period
as the Palæolithic period, without asserting that Palæolithic man
necessarily disappeared at the time when the climate changed and
caused the replacement of Steppe conditions by others favourable to
forest-growth.
_Description of the accumulations._ The loess consists of unstratified
calcareous mud or dust, with a peculiar vertical fracture, and is
interesting rather on account of the nature of its fossils and of its
distribution than for its lithological characters. As it is not found
in Britain it is not necessary to say much about it, but merely to
refer to the published descriptions[111].
[Footnote 111: An account of Richthofen's views by that author will be
found in the _Geological Magazine_, Dec. 2, vol. IX. (1882), p. 293,
and the fauna of the loess is described by Nehring (_Ibid._, p. 570).]
The British deposits require some notice, as their characters and mode
of occurrence are of some significance. Along the south coast are
deposits of coarse rubble which have yielded some organic remains,
which have been described by Mr Clement Reid[112], who also discusses
their origin. The rock, also known as the Elephant Bed, consists of
angular fragments of flint and chalk, and seems to have been produced
by streams which were able to flow over the surface of the chalk when
it was frozen. Many other similar deposits in the south of England,
which are found on the open surface, may have had a similar origin.
[Footnote 112: C. Reid, "Origin of Dry Chalk Valleys and of Coombe
Rock," _Quart. Journ. Geol. Soc._, vol. XLIII. p. 364.]
The Palæolithic river-gravels are found at various distances above
present river-levels, and are the surviving relics of alluvial
deposits which were laid down when the rivers ran at a higher level
than they now do. That they are newer than the main glacial drifts of
the region in which they occur is indicated by the frequent presence
in them of boulders derived from the drift. Their antiquity is shown
by the physical changes which have occurred since their deposition
(there having been sufficient time since then to allow of the
excavation of some river-valleys to a depth of over one hundred feet
beneath their former level), and also by the character of the included
mammals which will presently be referred to. The deposits vary in
coarseness, like those of modern alluvial flats, from the coarse
gravels of the river-beds to the fine loams and marls of the
flood-plains. They are found, in Britain, with their typical mammalian
remains, south-east of a line drawn from the mouth of the Tees to the
Bristol Channel.
The cave-deposits have a wider distribution than those which have just
been noticed, being also found to the north-west of the
above-mentioned line in Yorkshire, and in North and South Wales. In
the south of England they are found as far east as Ightham in Kent,
and in a westerly direction to Torquay and Tenby. The Ightham deposits
occur in fissures and consist of materials which were apparently
introduced from above by river action[113]. The cave-deposits of
limestone areas are sometimes found in fissures, but at other times in
caverns with a fairly horizontal floor, on which the various
accumulations lie in order of formation. The deposits vary in
character and may be divided into three groups, though accumulations
of intermediate character are found; the first group consists of
cave-earths and cave-breccias--formed by weathering of the limestone,
and the retention of the insoluble residue, as a more or less
ferruginous mud, mixed with angular fragments of limestone, and with
the remains of creatures which inhabited the caves; the second group
consists of true deposits laid down under water, as gravels, sands,
and laminated clays; while the third is composed of limestone
deposited from solution in water, in the form of stalagmite[114].
[Footnote 113: The Ightham fissures and their contents are described
by Messrs Abbot and Newton, _Quart. Journ. Geol. Soc._, vol. L. pp.
171 and 188.]
[Footnote 114: The reader should consult Prof. W. Boyd Dawkins' works
on _Cave Hunting_ and _Early Man in Britain_, for information
concerning the Cave Deposits. See also Sir C. Lyell, _Antiquity of
Man_; Sir J. Evans, _Ancient Stone Implements of Great Britain_, and
Sir J. Lubbock, _Prehistoric Times_. In these works references will be
found to papers by Messrs Pengelly, Magens Mello, Tiddeman and others
on the Caves of Devon, Derbyshire and Yorkshire. References have
already been made to papers upon the Caverns of North Wales.]
The organic contents of the Palæolithic period are of much interest,
and it is desirable to discuss their character before making further
observations upon the physical conditions of the period.
_The Palæolithic flora and fauna._ The plants of some of the earlier
deposits of the age we are considering show the prevalence of cold
conditions during their accumulation, for instance the Arctic birch
and Arctic willow are found in the accumulations beneath the
implement-bearing Palæolithic deposits of Hoxne in Suffolk[115]. The
invertebrate fauna consists essentially of the remains of molluscs.
The loess molluscs are chiefly pulmoniferous gastropods which lived
upon the land, though swamp forms are occasionally associated with
them. The palæolithic river-gravels have yielded numerous land- and
freshwater-molluscs of living species, though some which are abundant
in the British gravels are now extinct in Britain, e.g. _Cyrena
(Cobicula) fluminalis_ and _Unio littoralis_. Marine deposits of this
age are occasionally found, as at March, in Cambridgeshire, where the
fauna closely resembles that of our present sea-shores.
[Footnote 115: These beds are described by Messrs Reid and Ridley,
_Geol. Mag._ Dec. III. vol. V. p. 441. See also C. Reid on the
"History of the Recent Flora of Britain," _Annals of Botany_, vol. II.
No. 8, Aug. 1888.]
The vertebrate remains are much more remarkable, and it is not quite
clear that the association of forms whose living allies now live under
widely different conditions has been satisfactorily explained. The
river-gravels and cave-deposits contain remains of temperate forms, as
the bison, and brown bear, associated with those of northern forms, as
the mammoth, woolly rhinoceros, glutton, reindeer, and musk ox, and
also with those whose living allies are inhabitants of warmer regions,
like the lion, hyæna, and hippopotamus. One of the most remarkable
creatures is the sabre-toothed lion or _Machairodus_, remains of which
have been discovered in Kent's Cavern, Torquay, and in the caves of
Cresswell Crags, Derbyshire.
The loess fauna consists of characteristic steppe animals, such as the
jerboa, Saiga antelope and steppe-porcupine, and it is interesting to
find an indication of this fauna in the Ightham fissures.
The first undoubted relics of mankind are found in the Palæolithic
deposits, which are very widely spread over the Eurasian continent.
They consist mainly of implements of bone and stone, the latter being
chipped, but never ground or polished, though both bone and stone
implements are frequently ornamented with engraved figures. The
cave-deposits have furnished implements of a higher type than those
usually found in the river-drifts, but the latter are also found in
caverns in deposits beneath those containing the higher type, hence
the division of the period into two minor periods, that of river-drift
man, and that of cave-man[116].
[Footnote 116: Concerning this matter, the reader should consult Prof.
Boyd Dawkins' _Early Man in Britain_. Sir J. Prestwich has argued in
favour of the existence of a group of implements found on the plateau
south of the Thames of an age antecedent to that of the ordinary
river-drift implements. See _Quart. Journ. Geol. Soc._, vol. XLV. p.
270.]
There are several questions of interest connected with the Palæolithic
fauna, three of which deserve some notice here. The absence of the
relics of the Palæolithic mammalia and of the human implements in the
river-gravels north-west of the line drawn between the Tees and
Bristol Channel, and the presence of the mammalian remains in the
caverns of that area requires some explanation. One such explanation
assumes that the relics were destroyed in the open country to the
north-west of that line, owing to glaciation, but it is not by any
means universally accepted.
Another difficulty which in the opinion of some writers has not been
fully cleared up is the mixture of apparently southern forms like the
Hippopotamus, with others of northern character like the Musk ox,
under such conditions as to show that the creatures lived in the
British area contemporaneously. Seasonal migration might account for
it, but the wide belt of overlap of apparent northern and southern
forms requires something more, though secular changes of climate might
shift the belt of seasonal overlap from one place to another, causing
the entire belt of overlap to extend over a considerable distance.
The third, and perhaps most important difficulty is the abrupt change
from the Palæolithic type of implement to the Neolithic type,
characteristic of the next period. Some implements, as those of the
kitchen-middens of Denmark, and those found at Brandon and Cissbury in
this country, have been appealed to as intermediate in character, but
evidence has been brought forward to show that each set is truly
Neolithic, the one being the implements of the lowly fisher-folk who
lived contemporaneously with the makers of the highly finished
polished implements of Denmark, while the others are unfinished
implements thrown away during the manufacture on account of flaws or
accidental fractures. The difficulty is increased when we take into
account the great physical and faunistic changes which occurred
between Palæolithic and Neolithic times.
The country was undoubtedly more elevated than it is at present during
portions if not during the whole of Palæolithic times, as shown by the
appearance of the great mammals in Britain, the discovery of their
remains beneath sea-level, and especially the occurrence of remains in
the caverns of rocky islands such as those of the Bristol Channel,
where they could not possibly have existed unless the present islands
were connected with the mainland.
The fossils of the times between the Glacial period and the Neolithic
period indicate variations of climatic conditions. Upon this point I
cannot do better than quote the words of Sir John Evans in his
Presidential Address to the British Association at Toronto[117]. "At
Hoxne the interval between the deposit of the Boulder clay and of the
implement-bearing beds is distinctly proved to have witnessed at least
two noteworthy changes in climate. The beds immediately reposing on
the clay are characterised by the presence of alder in abundance, of
hazel, and yew, as well as by that of numerous flowering plants
indicative of a temperate climate very different from that under which
the Boulder clay itself was formed. Above these beds characterised by
temperate plants, comes a thick and more recent series of strata, in
which leaves of the dwarf Arctic willow and birch abound, and which
were in all probability deposited under conditions like those of the
cold regions of Siberia and North America.
"At a higher level, and of more recent date than these--from which
they are entirely distinct--are the beds containing the Palæolithic
implements, formed in all probability under conditions not essentially
different from those of the present day."
[Footnote 117: _Report Brit. Assoc._ for 1897, p. 13.]