Mar. 5, 1874J 



NATURE 



339 



sisted on by the Lord Rector will find place, can easily be 

 found ; methods against which no objection can be urged, 

 and from tlie application of which a tremendous increase 

 in the rate of advancement of knowledge in this country 

 may be anticipated. 



POST-TERTIARY GEOLOGY* 

 The Great Icc-Age and its relation to the Antiquity of 

 Man. By James Geikie. (W. Isbister and Co. 1874.) 



ir. 



WE must next turn to beds which furnish conclusive 

 proof of a return of cold conditions, the well-known 

 shell-bearing clays found here and there along the coast of 

 Scotland. The fossils and the physical condition of these 

 beds both concur in telling the same tale, that an Arctic 

 climate again prevailed in Britain. These deposits are 

 marine, and have not been met with at a greater height 

 above the sea than 360 feet, and they were therefore 

 formed towards the termination of the period during 

 which the land was emerging from the sea. Evidence of 

 a similar change of climate is, however, found in the in- 

 terior of the country. In the Highland glens and the 

 high valleys of the Southern Uplands morainic deposits, 

 distinguishable from those of the earlier ice period, are of 

 common occurrence, sometimes scattered loosely over the 

 mountain slopes, sometimes arranged in ridges or lines of 

 mounds across the valleys after the fashion of terminal 

 moraines. The climate, therefore, must have become 

 again severe enough to allow of the accumulation of ice ; 

 but, since the second set of glaciers is shown by the 

 moraines which they have left behind them to have been 

 confined to the high ground, and each restricted to its 

 own valley, the cold must have been far less intense than 

 during the period of the first glaciation. 



The second period of cold, however, passed away, and 

 the record of its gradual disappearance is written for us in 

 this way. In many of the upland valleys concentric lines of 

 mounds, each marking the terminal moraine of a glacier, 

 are arranged one within the other, and as we ascend 

 these piles are found to grow more and more puny, till 

 they at last vanish altogether. From this we see, as 

 clearly as if the operation had gone on before our eyes, 

 how each glacier shrank back step by step into the heart 

 of the mountain glens, and at last yielded to the gradual 

 amelioration of the climate, and melted entirely away. 

 Another train of reasoning leads us to the same conclu- 

 sion. The rising of the land was not continuous, but 

 broken every now and then by pauses, and during each 

 of these the sea cut a notch or shelf in the rocks and oc- 

 casionally spread out terraces of shingle and silt, forming 

 what are known as Raised Beaches. These beaches 

 occur at many different levels, from 1,500 feet down to a 

 few yards above the mean-tide level. The higher of 

 these beaches furnish evidence of somewhat Arctic con- 

 ditions, but as we descend in the series these traces be- 

 come less pronounced. 



We are now approaching the close of the glacial epoch, 

 and the climate, though still colder than now, was ap- 

 proximating to what it is at present. 



The author goes on to show, from a consideration of 

 submerged forests, how the elevation of the land went on 



* Continued fro p. ^21, 



till Britain was raised above its present level, and probably 

 connected by a land surface with the mainland of Europe ; 

 and points out how the continental climate thus produced 

 will account for the dense forests which formerly clothed 

 our island, while a return to insular conditions resulted 

 in a decay of the woods and the growth of peat mosses. 



Lastly, our country became again dissevered from the 

 continent, and the submergence which brought about this 

 change went on till the land was sunk somewhat below its 

 present level ; while it rose into its present position, low 

 level raised beaches were formed, among which the well- 

 known 25-feet-beach is most conspicuous. 



Such then is the succession of physical changes which 

 the Drift-deposits show has taken place in our island. 



The author has passed in review also the contempo- 

 raneous formations of Scandinavia, Switzerland, and 

 North America, and pointed out how the story they tell 

 agrees in its main features with that deduced from our 

 own glacial formations. 



- Had he done no, more than' this he would have pro- 

 duced a work of surpassing interest and value, but the 

 concluding chapters of his book will perhaps attract more 

 attention than any other part of it, for they deal with a 

 question that comes in a measure personally home to us, 

 the antiquity of man and the date of his first appearance 

 in Britain. 



The oldest races of men of which traces have yet been 

 discovered are known as the Stone-folk, because they 

 fashioned their implements out of stone and seem to have 

 been unacquainted with the use of metals. These Stone- 

 folk are clearly distinguishable into two classes — the older, 

 known as Pateolithic, merely chipped stones into shape ; 

 the later, or Neohthic, had advanced a step farther, and 

 constructed tools highly polished and otherwise more 

 finished than those of their predecessors. We also find 

 associated with the traces of Paleolithic man a group of 

 mammals now wholly or locally extinct, while the 

 mammals accompanying the remains of Neolithic man 

 are many of them still indigenous to the country. In con- 

 nection with this subject the author has brought promi- 

 nently into notice a fact which had not received the atten- 

 tion it deserves, that nowhere [have any signs been de- 

 tected of gradual improvement on the part of PalsEolithic 

 man, by which he may have passed from abject barbarism 

 to the more advanced skill of his Neolithic successor, but 

 that, on the contrary, the two races are everywhere sharply 

 marked off from one another. In the same way the 

 accompanying groups of mammals are essentially distinct, 

 and we nowhere find traces of the dying out of the one 

 and the gradual coming in of the other. But one in- 

 ference can be drawn from these facts : between the time 

 when the Palajolithic race inhabited Britain and the coming 

 in of the Neolithic race a long mterval must have elapsed, 

 during which man was by some means or other driven 

 out of the country, and went through elsewhere the long 

 series of modifications by which he was himself advanced 

 in civilisation, while at the same time the group of ani- 

 mals associated with him became totally changed. Now 

 we know of no physical change since the second glaciation 

 of the country which could have been the cause of such a 

 migration, for all the evidence both here and elsewhere 

 tends to show, that whatever change of climate has oc- 

 curred between that event and the present day has been 



