the Displacement of Shore-lines. 491 



and Cretaceous ; and he says further : — " I believe that the 

 study of fossils from remote parts of the earth's surface has 

 abundantly substantiated Prof. Huxley's suggestion that geo- 

 graphical provinces and zones may have been as distinctly 

 marked in the Palseozoic epoch as at present." 



Most deposits of ancient times belong to periods in which 

 the land lay low in relation to the sea, and the difference 

 between the geographical provinces is far less in the great 

 depths of the sea than near the shores and on the solid ground. 

 It has also hitherto been a general theory that the climate in old 

 times was w^armer and more uniform over the whole earth 

 than now. The further we go back, it is said, the warmer it 

 was, and this has been regarded as connected with the interior 

 heat of the earth. The Grlacial period was an interruption of 

 the continuity of its gradual cooling. In periods of over- 

 flow, when the land lay iow^ and the sea had great exten- 

 sion under high latitudes, warm marine currents had much 

 easier access to the Poles than during continental periods. 

 As we now know most about the deposits formed during 

 periods of overflow, and as most of the deposits of continental 

 periods are either removed by denudation or concealed under 

 the sea, it is still probable that the deposits of older cycles 

 might show less strongly marked geographical provinces, and, 

 as a rule, bear witness to warmer climates even under high 

 latitudes. But the great changes in the distribution of land 

 and sea compel us to assume that, hand in hand with them, 

 occurred a periodical alteration of climate, which has been far 

 greater and more radical than the change produced by the 

 precessional periods. 



Ramsay, Croll, J. Geikie, and others have thought that 

 they found more or less certain traces of Glacial periods in the 

 older formations (see, e. g., J. Geikie, ' The Great Ice Age,' 

 ed. 2, 1887, pp. 566 et seqq.). Some of these traces seem to 

 prove that, at any rate, there have been more Glacial periods 

 than the Post-tertiary one. Nevertheless von Richthofen 

 remarks (^Filhrer fur Forschungsreisende, p. 362) that these 

 supposed traces of Glacial periods are perhaps only a pheno- 

 menon of abrasion, and that the action of the waves upon the 

 shore could produce conglomerates with striated stones. As 

 regards these supposed old Glacial periods, the most certain 

 traces (see J. Geikie, /. c.) appear to be furnished by the 

 Devonian Sandstone, " Old Red," in England and Scotland, 

 by the commencement of the Carboniferous i)eriod (Scotland), 

 by the Permian conglomerate (England), and by the Eocene 

 (Switzerland). The most striking evidence (with striated 

 stones) is from the periods when the land had great extension. 



