NA TURE 



>85 



THURSDAY, AUGUST 24, 1893. 



WATER AND ICE AS AGENTS OF EARTH 

 SCULPTURE. 



Fragments of Earth Lore : Sketches and Addresses, 

 Geological and Geographical. By James Geikie, 

 D.C.L., LL.D., F.R.S., &c., &c. (Edinburgh : John 

 Bartholomew & Co. London : Simpkin Marshall, 

 Hamilton, Kent & Co., Limited, 1893.) 



THESE collected papers form a fairly connected 

 work on the origin of the present surface features 

 of the world at large, and of Scotland in particular. The 

 first is a well- put plea for the more intelligent and far- 

 sighted method of teaching geography, and is followed 

 up by four articles on the geographical features of Scot- 

 land, which are of a somewhat advanced and special 

 character, and lead directly to the exposition of the 

 author's views on glacial action. That forms the subject 

 matter of the next eight papers, supplemented by a 

 geographical essay in which he discusses some aspects 

 of the question of earth movements, which are obviously 

 closely connected with the theoretical explanations of 

 climatal change. On the whole, perhaps, another form 

 would have been better ; for the advice as to the teach- 

 ing of geography will hardly be necessary for the 

 same readers as those who, with their local field 

 club, are prepared to follow the author through the 

 Western Islands ; while those who wish to examine 

 once more the arguments for the special views on the 

 ancient glaciation of the country which he advocates, 

 would have found the information more usefully arranged 

 for them, if worked into a manual. The style of the 

 articles is sufficiently didactic to have readily lent itself 

 to this form. 



The book provides for the author an inventory of his 

 own literary properties, and of some others, in which he 

 has a joint claim, owing to his having independently 

 arrived at the same conclusion as other observers. It 

 provides for him also an opportunity of qualifying state- 

 ments which further investigation has shown to require 

 modification. In which respect the reader is equally 

 benefited, as he would certainly prefer to receive the 

 results of our author's mature judgment on the subject. 



We appeal to him as a leader in geographical science, 

 and one who has abundant facility of expression, 

 not to encourage the absorption of too many words 

 out of our current language for use as technical terms. 

 Such names as chain and range should be simply de- 

 scriptive of form, that is of actual continuity, or of con- 

 tiguity with a linear arrangement, regardless of the origin 

 of the features. 



Among the most interesting geographical descriptions 



iven is that of the "drowned lands," or areas which 



ive been moulded into their present form by subasrial 



lion, and then submerged with all their hills and valleys 



;^p. 21, 367, and more fully in art. xiv). We shall know 



more about this as we get more soundings and the study 



of oceanography advances. 



The feature of greatest importance in the study of 

 ge ology and geography is the plain of marine denuda- 

 tion, the level at which the sea arrests the agents of 

 i NO, "43 VOL. 48] 



subaerial waste, and at which the wind waves carry on 

 the work. This is the datum from which the amount of 

 rock removed by denudation must be measured : this is 

 the index that tells us how long the great forces of eleva- 

 tion and depression balanced one another : this marks 

 the long drawn-out nodes in the undulations of the earth's 

 crust. 



Our author might have dwelt longer on this ground, 

 when giving his views as to ho.v the successive portions 

 of the earth were brought within reach of the denuding 

 agents to which he chiefly refers their sculpture. 



Most of the papers are controversial, or they are 

 written so as to strengthen those positions on which some 

 disputed theory has been built up, and are so turned as 

 to allow the author frequently to point the moral which 

 he chiefly aims at inculcating. 



We feel quite glad of the genial warmth of the volcanic 

 fires which ushered in the Devonian, and are hardly willing 

 to admit the existence of ice at this age in the Cheviot area. 

 Yet there is no reason why the surrounding mountains 

 may not have been high enough to nourish glaciers, but the 

 shape and condition of the stones included in the con- 

 glomerates at the base of the red rocks are hardly sufficient 

 to prove this, especially when the ghosts of scratches 

 have in other cases been shown to be due to movements 

 in the rock, which caused the included fragments to be 

 crushed against one another. 



After a long interval we read in the history of the Cheviots 

 of Scandinavian ice which over-rode everything, and of the 

 successive interglacial periods when that ice receded only 

 to advance again with hardly less intensity, but we do 

 not know how our author explains its apparently smaller 

 eroding power, seeing that it failed to remove even the 

 peat and silt which had accumulated in the interval. 



As an example of the kind of evidence which is occa- 

 sionally admitted in support of the former extension of 

 land ice we may cite his reference of the implement- 

 bearing gravels of East Anglia to the floods discharged 

 at the foot of the melting ice-sheet. 



The argument that the gravels are eighty feet above 

 the sources of the existing streams after ages of denuda- 

 tion does not go for much where the level of the outburst 

 of springs has varied within the memory of man ; while 

 the flint implement-bearing gravels creep up the hills in 

 terraces with abundant material derived from the boulder 

 clay which covers the tops of the hills all round, but 

 never overlaps those gravels. The shells in the gravels 

 are, with few exceptions, of the same species as those now 

 inhabiting the neighbouring streams, and those excep- 

 tions belong to more southern forms. There very likely 

 are marine gravels capping some hills, but they are cer- 

 tainly not correctly referred to as those " with ancient 

 flint implements," &c., in East Anglia. 



Although he frequently mentions '' the now discredited 

 iceberg theory," he does not often refer any of the drifts 

 to their " random and eccentric action," but explains some 

 of the difficulties of the distribution of erratics by the 

 intercrossing of currents within the ice-mass. Whether 

 or not any particular group of boulders or mass of drift 

 was carried by icebergs or not, it is too much to say that 

 there are no reasons for considering icebergs capable of 

 polishing and striating rock surfaces (p. 219). If we 

 allow that glacier-ice charged with stones and mud can 



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