[Footnote 11: The most important discovery of recent years in this connection is that made in Suss.e.x by Mr. C. Dawson and Dr. A. Smith Woodward; this find is described in great detail in the "Quarterly Journal of the Geological Society," volume 69, 1913, pages 117 to 151.

At a height of about 80 feet above the present level of the River Ouse, at Piltdown, near Uckfield, is a gravel, containing many brown flints of peculiar character, some of which are implements of Ch.e.l.lean or earlier type, a.s.sociated with some remains of Pleistocene animals and a few of older date, derived from Pliocene deposits. Embedded in this gravel were found fragments of a human skull and lower jaw of very remarkable type, showing in some respects distinctly simian characters, while in other respects it is less ape-like than the Mousterian skulls of Neanderthal and other localities. For this form the name of Eoanthropus has been proposed, thus const.i.tuting a new genus of the Hominidae.]

[Footnote 12: It will be well at this point to give a brief summary of the modern cla.s.sification of the Palaeolithic implement-bearing deposits of Europe. From the labours of many geologists and prehistoric archaeologists, especially in France, a definite succession of types of implement has been established, and in some cases it has been found possible to correlate these with actual human remains and with certain well-marked events in the physical history of Pleistocene times, especially with the advance and retreat of ice-sheets. The present state of our knowledge is admirably summarised by Professor Sollas ("Ancient Hunters," London, 1911), and from that work the following note is condensed.

The stages of Palaeolithic culture now recognised are as follows:--

Azilian Magdalenian Solutrean Aurignacian Mousterian Acheulean Ch.e.l.lean Strepyan Mesvinian.

Below the Mesvinian comes the nebulous region of "eoliths," which are not yet definitely proved to be of human workmanship. The Neanderthal skull belongs to the Mousterian stage, but the oldest known definitely human remain, the jaw from the Mauer sands near Heidelberg, may be older than any of these, indeed by some it is a.s.signed to the first interglacial period of Penck and Bruckner (see Note 32). For figures of the types of implement characterising each period, see "Guide to the Antiquities of the Stone Age in the Department of British and Medieval Antiquities," British Museum, 2nd edition, London, 1911, pages 1 to 74.

This publication gives an admirable summary of recent knowledge on this subject. For an excellent and critical summary of the latest researches on Palaeolithic man up till the end of the Aurignacian period, see Duckworth, "Prehistoric Man," Cambridge, 1912. See also note 44.]

[Footnote 13: Sir John Evans, K.C.B. (1823-1908), was one of the foremost authorities on prehistoric archaeology and a prolific writer on the subject. His best known work is "The Ancient Stone Implements, Weapons, and Ornaments of Great Britain," 2nd edition, 1897.]

[Footnote 14: By the expression "Celtic weapons of the stone period" is presumably meant Neolithic implements, with polished surfaces.]

[Footnote 15: It has recently been shown that the growth of peat is a very slow process, and at the present time it is in many places either at a standstill or even in a state of retrogression. In the peat-mosses of Scotland, Lewis has traced nine successive layers, marked by different floras. The lowest of these and another at a higher level are distinctly of an arctic character, the intermediate forest beds, on the other hand, indicate periods of milder climate, when the limit of the growth of trees was at a higher level in Scotland than is now the case.

From these facts it is certain that the peat-mosses of Scotland and northern England date back at least as far as the later stages of the glacial period, and indicate at least one mild interglacial episode, when the climate was somewhat warmer than it now is. (See Lewis, "Science Progress," volume 2, 1907, page 307.) Hence the statements of the French workmen, here quoted, do not possess much significance.]

[Footnote 16: Cyrena fluminalis is very abundant in the gravels of an old terrace of the River Cam, at Barnwell, in the suburbs of Cambridge, and also in glacial gravels at Kelsey Hill in Holderness. It is a very remarkable fact that this sh.e.l.l, now an inhabitant of warm regions, should be so abundant in these Pleistocene deposits, in close a.s.sociation with glacial acc.u.mulations.]

[Footnote 17: The implement-bearing deposits of Hoxne, in Suffolk, were investigated with great care by a committee of the British a.s.sociation, and the results were published in a special and detailed report ("The Relation of Palaeolithic Man to the Glacial Epoch," "Report of the British a.s.sociation," Liverpool, 1896, pages 400 to 415). The deposit consists of a series of lacustrine or fluviatile strata with plant remains, some being arctic in character, resting on Chalky Boulder Clay, and this again on sand. The Palaeolithic deposits are all clearly later than the latest boulder-clay of East Anglia, and between their formation and that of the glacial deposits at least two important climatic changes took place, indicating a very considerable lapse of time.

Mention may conveniently be made here of the supposed discovery of the remains of pre-glacial man at Ipswich, which appears to be founded on errors of observation. The boulder-clay above the interment is, according to the best authorities, merely a landslip or flow.]

[Footnote 18: It has been suggested with a considerable degree of probability, that in Auvergne volcanic eruptions persisted even into historic times. The subject is obscure, depending on the interpretation of difficult pa.s.sages in two Latin chronicles of the fifth century. The most obvious meaning of both pa.s.sages would certainly appear to be the occurrence of volcanic eruptions and earthquakes, but attempts have been made to explain them as referring to some artificial conflagration, possibly the burning of a town by an invader. (See Bonney, "Volcanoes,"

3rd edition, London, 1913, page 129.)]

[Footnote 19: In the early days of glacial geology in Britain, it was commonly accepted that the phenomena could be most satisfactorily explained on the hypothesis of a general submergence of the northern parts of the country to a depth of many hundreds of feet, and this in spite of the original comparison by Aga.s.siz of the glacial deposits of Britain to those of the Alps. In later times, however, a school of geologists arose who attributed the glaciation of Britain to land-ice of the Continental or Greenland type. Of late years this school has been dominant in British geology, with a few notable exceptions, of whom the most important is Professor Bonney. The difficulties presented by both theories are almost equally great, and at the present time, in spite of the vehemence of the supporters of the land-ice theory, it is impossible to hold any dogmatic views on the subject. Against the doctrine of submergence is the absence of glacial deposits in places where they would naturally be expected to occur if the whole of the British Isles north of the Thames and Bristol Channel had been covered by the sea, together with the very general absence of sea-sh.e.l.ls in the deposits.

The objections to the land-ice hypothesis are largely of a mechanical nature. If we take into account the lateral extent and the thickness that can be a.s.signed to the ice-sheet, we are at once confronted by very considerable difficulties as to the sufficiency of the driving-power behind the ice. Another great difficulty is the shallowness of the North Sea, in which a comparatively thin ma.s.s of ice would run aground at almost any point. It has been calculated that the maximum slope of the surface of the ice from Norway to the English coast could not exceed half a degree, and it is therefore difficult to see what force could compel it to move forward at all, much less to climb steep slopes in the way postulated by the extremists of this school.]

[Footnote 20: The most complete account of the geology of the Norfolk coast is contained in "The Geology of Cromer," by Clement Reid ("Memoir of the Geological Survey"). (See also Harmer, "The Pleistocene Period in the Eastern Counties of England," "Geology in the Field, the Jubilee Volume of the Geologists a.s.sociation," 1909, chapter 4.). Above the Norwich Crag several more subdivisions are now recognised, and the complete succession of the Pliocene and Pleistocene strata of East Anglia may be summarised as follows:--

Pleistocene: Peat and Alluvium Gravel Terraces of the present river systems Gravels of the old river-systems Plateau gravels Chalky boulder-clay Interglacial sands and gravels and Contorted Drift Cromer Till Arctic Plant Bed.

Pliocene: Cromer Forest Series Weybourn Crag Chillesford Crag Norwich Crag Red Crag Coralline Crag.

[Footnote 21: It is now generally agreed that the tree-stumps in the Cromer Forest bed are not in the position of growth. Many of them are upside down or lying on their sides, and they were probably floated into their present position by the waters of a river flowing to the north.

This river was a tributary of the Rhine which then flowed for several hundred miles over a plain now forming the bed of the North Sea, collecting all the drainage of eastern England, and debouching into the North Atlantic somewhere to the south of the Faroe Isles. (See Harmer, "The Pleistocene Period in the Eastern Counties of England," "Geological a.s.sociation Jubilee Volume," London, 1909, pages 103 to 123.)]

[Footnote 22: Of late years an enormous number of characteristic rocks from Norway and Sweden have been recognised in the drifts of Eastern England, as far south as Ess.e.x and Middles.e.x. One of the most easily identifiable types is the well-known Rhombporphyry of the Christiania Fjord, a rock which occurs nowhere else in the world, and is quite unmistakable in appearance. Along with it are many of the distinctive soda-syenites found in the same district, the granites of southern Sweden, and many others. The literature of the subject is very large, but many details may be found in the annual reports of the British a.s.sociation for the last twenty years.]

From a study of these erratics it has been found possible to draw important conclusions as to the direction and sequence of the ice streams which flowed over these regions during the different stages of the glacial period.]

[Footnote 23: During his first crossing of Greenland from east to west, Nansen attained a height of 9000 feet on a vast expanse of frozen snow, and it is believed that towards the north the surface of this great snow-plateau rises to even greater elevations. The surface of the snow is perfectly clean and free from moraine-material. No rock in situ has been seen in the interior of Greenland at a distance greater than 75 miles from the coast.

A great amount of valuable information concerning the glacial conditions of Greenland is to be found in the "Meddelelser om Gronland," a Danish publication, but containing many summaries in French or English. For a good account of the phenomena seen in the coastal region of the west coast, see Drygalski, "Gronland-Expedition," a large monograph published by the Gesellschaft fur physischen Erdkunde, Berlin, 1897.]

[Footnote 24: The argument is here considerably understated. The southern point of Greenland, Cape Farewell, is in the same lat.i.tude as the Shetland Islands and Christiania, and only one degree north of Stockholm; Disko is in about the same lat.i.tude as the North Cape. Hence the inhabited portion of Greenland is in the same lat.i.tude as Norway and Sweden, both fertile and well-populated countries. Even in Central Norway, in the Gudbrandsdal and Romsdal, thick forests grow up to a height of at least 3000 feet above sea-level, a much greater elevation than trees now attain in the British Isles. This latter fact is probably to be attributed to the protective effect of thick snow lying throughout the winter.]

[Footnote 25: For a summary of the most recent views as to the cla.s.sification and succession of the glacial deposits of the British Isles, see Lake an Rastall, "Textbook of Geology," London, 1910, pages 466 to 473. Reference may also be made to Jukes-Browne, "The Building of the British Isles," London, 1912, pages 430 to 440.]

[Footnote 26: Glacier-lakes are fairly common among the fjords of the west coast of Greenland, and ill.u.s.trate very well what must have been the state of affairs in Glen Roy at the time of formation of the Parallel Roads.]

[Footnote 27: The high-level sh.e.l.l-bearing deposits of Moel Tryfan, Gloppa, near Oswestry, and Macclesfield, have given rise to much controversy between the supporters of submergence and of land-ice. At Moel Tryfan certain sands and gravels, with erratics, at a height of about 1350 feet, contain abundant marine sh.e.l.ls, generally much broken.

The northern or seaward face of the hill is much plastered with drift, but none is to be found on the landward side, and it is suggested that the sh.e.l.l-bearing material is the ground-moraine of a great ice-sheet that came in from the Irish Sea, and was forced up on to the Welsh coast, just reaching the watershed, but failing to overtop it. With regard to the explanation by submergence, the great objection is the absence of marine drift on the landward side, which is very difficult to explain if the whole had been submerged sufficiently to allow of normal marine deposits at such a great height. The sh.e.l.l beds of Macclesfield and Gloppa are at a less elevation but of essentially similar character.

The sh.e.l.l-bearing deposits of Moel Tryfan were examined by a committee of the British a.s.sociation. (See "Report of the British a.s.sociation"

Dover, 1899, pages 414 to 423.) At the end of this report is an extensive bibliography.]

[Footnote 28: During the last forty years the deep-sea dredging expeditions of H. M.S. Challenger and others have shown the abundance and variety of animal life at great depths, especially in the Arctic and Antarctic seas. For a recent summary, see Murray and Hjort, "The Depths of the Ocean," London, 1912.]

[Footnote 29: It is now generally admitted that these sh.e.l.l-beds in Wexford are of Pliocene age, and they therefore have no bearing on the subject under discussion.]

[Footnote 30: The boulder deposit at Selsey has been described by Mr.

Clement Reid ("Quarterly Journal of the Geological Society," volume 48, 1892, page 355). Immediately above the Tertiary beds is a hard greenish clay, full of derived Tertiary fossils and Pleistocene sh.e.l.ls with large flints and erratic blocks, some of the latter weighing several tons.

They include granite, greenstone, schist, slate, quartzite, and sandstone, and most of them must have been transported for a long distance. Above them are black muds with marine sh.e.l.ls, then a shingle beach, and above all the Coombe Rock. (See next note.)]

[Footnote 31: The Brighton elephant-bed and its equivalent, the Coombe Rock, are fully described by Clement Reid ("On the Origin of Dry Chalk Valleys and the Coombe Rock," "Quarterly Journal of the Geological Society," volume 43, 1887, page 364). The Coombe Rock is a ma.s.s of unstratified flints and Chalk debris filling the lower parts of the dry valleys (Coombes) of the South Downs and gradually pa.s.sing into the brick-earth (loam) of the coastal plain. It is clearly a torrential acc.u.mulation, and is supposed to have been formed while the Chalk was frozen, thus preventing percolation of water and causing the surface water to run off as strong streams. This must have occurred during some part of the glacial period, which would naturally be a period of heavy precipitation. Of very similar origin is the "Head" of Cornwall, a surface deposit often rich in tinstone and other minerals of economic value. The Coombe Rock has recently been correlated with deposits of Mousterian Age.]

[Footnote 32: The former extension of the Alpine glaciers and the deposits formed by them have been exhaustively investigated by Penck and Bruckner ("Die Alpen im Eiszeitalter," 3 volumes, Leipzig, 1901 to 1909). In this monumental work the authors claim to have established the occurrence of four periods of advance of the ice, to which they give the names of Gunz, Mindel, Riss, and Wurm glaciations, with corresponding interglacial genial episodes, when the climate was possibly even somewhat warmer than now. Their conclusions and the data on which they are established are summarised by Sollas (" Ancient Hunters," London, 1911, especially pages 18 to 28). For a general account of the glaciers of the Alps and their accompanying phenomena, see Bonney, "The Building of the Alps," London, 1912, pages 103 to 151.]

[Footnote 33: At the time of the maximum advance of the ice, during the Riss period of Penck and Bruckner, the terminal moraine of the great glacier of the Rhone extended as far as the city of Lyon, and towards the north-east it became continuous with the similar moraine of the Rhine glacier.]

[Footnote 34: For the successive phases of advance and retreat of the Alpine glaciers, see the works quoted in Note 32.]

[Footnote 35: The Loess of Central Europe includes deposits of two different ages. According to Penck the "Older Loess" was formed in the period of warm and dry climate that intervened between the third and fourth glacial episodes, while the "Younger Loess" is post-glacial.

Both divisions are for the most part aeolian deposits, formed by the redistribution of fine glacial mud originally laid down in water and carried by the wind often to considerable heights. A part, however, of the so-called Loess of northern France, e.g. in the valley of the Somme, is rain-wash, similar in character to the brick-earth of parts of south-eastern England. The Older Loess contains Acheulean implements, while the Younger Loess is of Aurignacian Age.

The greatest development of the Loess is in Central Asia and in China.

(See Richthofen, "China," Berlin, 1877.) In China the Loess reaches a thickness of several thousand feet, and whole mountain-ranges are sometimes almost completely buried in it. In the deserts of Central Asia the formation of the Loess is still in progress. A very similar deposit, called adobe, is also found in certain parts of the Mississippi valley.

The Loess is a fine calcareous silt or clay of a yellowish colour, quite soft and crumbling between the fingers. However, it resists denudation in a remarkable manner, and in China it often stands up in vertical walls hundreds of feet in height. This property is probably a.s.sisted by the presence of numerous fine tubes arranged vertically and lined with calcium carbonate; these are supposed to have been formed in the first place by fibrous rootlets.]

[Footnote 36: Although highly probable, it cannot yet be regarded as conclusively demonstrated that the Pleistocene glaciations of Europe and of North America were exactly contemporaneous. The ice--sheets in each case radiated from independent centres which were not in the extreme north of either continent, and were not in any way connected with a general polar ice-cap. The European centre was over the Baltic region or the south of Scandinavia, and the American centre in the neighbourhood of Hudson's Bay. The southern margin of the American ice-sheet extended about as far south as lat.i.tude 38 degrees north in the area lying south of the Great Lakes, whereas the North European ice barely pa.s.sed the limit of 50 degrees north in Central Europe. This greater southward extension in America was doubtless correlated with the same causes as now produce the low winter temperatures of the eastern states, especially the cold Newfoundland current. The literature of North American glacial geology has now attained colossal dimensions, and it is impossible to give here even a short abstract of the main conclusions.

For a general summary reference may be made to Chamberlin and Salisbury, "Geology," volume 3; "Earth History," London and New York, 1905; or the same authors' "Geology, Shorter Course," London and New York, 1909.]

[Footnote 37: During the last fifty years scarcely any geological subject has given rise to a greater amount of speculation than the cause of the Ice Age, and the solution of the problem is still apparently far off. The theories put forward may for convenience be divided into three groups, namely astronomical, geographical, and meteorological.

As examples of astronomical explanation, we may take the well-known theory of Adhemar and Crohl, which is founded on changes in the ellipticity of the earth's...o...b..t. This is expounded and amplified by Sir Robert Ball in his "Cause of an Ice Age." The weak point of this theory, which is mathematically una.s.sailable, is that it proves too much, and postulates a constant succession of glacial periods throughout earth-history, and for this there is no evidence. The geographical explanations are chiefly founded on supposed changes in the distribution of sea and land, with consequent diversion of cold and warm currents.

Another suggestion is that the glaciated areas had undergone elevation into mountain regions, but this is in conflict with evidence for submergence beneath the sea in certain cases. Meteorological hypotheses, such as that of Harmer, founded on a different arrangement of air pressures and wind-directions, seem to offer the most promising field for exploration and future work, but it is clear that much still remains to be explained.]

[Footnote 38: The reptile-bearing Elgin Sandstones are of Tria.s.sic Age, and they contain a most remarkable a.s.semblage of strange and eccentric forms, especially Anomodont reptiles resembling those found in the Karroo formation of South Africa.]

[Footnote 39: The meaning of this statement is not very clear. The Conifers are not dicotyledons: their seeds contain numerous cotyledons, up to twenty in number, and the whole plant, and especially the reproductive system, belongs to a lower stage of development. The argument here employed is therefore fallacious, and in point of fact the different groups actually appeared in the order postulated by the theory of evolution, namely: (1) Gymnosperms, (2) Monocotyledons, (3) Dicotyledons. See Arber, "The Origin of Gymnosperms," "Science Progress," volume 1, 1906, pages 222 to 237.]

[Footnote 40: The part of the ma.n.u.script read to Dr. Hooker in 1844 was undoubtedly the "Essay of 1844," forming the second part of the "Foundations of the Origin of Species," a volume published by Sir Francis Darwin on the occasion of the Darwin Centenary at Cambridge in 1909. (See also Darwin's "Life and Letters," volume 2 pages 16 to 18.)]