ON THE MOVEMENTS OF THE ExVRTH's CRUST. 349 



considerable changes of climate, and at the same time also changes of 

 living forms. I have already, in one of my memoirs, put forward the 

 opinion that the glacial period had its origin in a change of the distri- 

 bution of land and sea. If the laud gained a great extension in the 

 middle and higher latitudes, especially if there should be a formation 

 of bridges across the sea such as the supposed bridge through the FaWies 

 and Iceland from Scotland to (xreenland, the warm sea-currents would 

 be excluded from the higher latitudes. The northern seas would then 

 become icy seas, and where the snow-fall is sufficiently inland ice would 

 be formed. In a memoir entitled "Natiirliche Warmwasserheizung als 

 Princip der klimatischen Zustiinde der geologischen Formatiouen" (in 

 Abhandl. Senclcenh, Gesellsch. vol. xiii, p. 277 et seq.), J. Probst (like Sar- 

 torius von Waltershausen, in his Unterfmchuniienuher die Klimaie der 

 Gegenwart und Vergangenhcit, 1865) has with justice pointed out the 

 great importance which warm sea-currents have, and have had, in ren- 

 dering milder the climate of high latitudes. 



It has been generally accepted among geologists that during the older 

 formations animal and plant life was more uniform over the whole earth 

 than at present. But this opinion must be changed according to recent 

 investigations. Thus J. W. Judd says {Mature, March 1, 1888, pp. 424 

 et seq.), with regard to the oldest fossiliferous deposits (the Cambrian) : 

 " Even at that early period there were life -provinces with a distribu- 

 tion of organisms in space quite analogous to that which exists at the 

 present day." Examples of geographical provinces are indicated by 

 him in the Silurian, Trias, Jura, and Cretaceous; and he says further: 

 " I believe that the study of fossils from remote parts of the earth's sur- 

 face has abundantly substantiated Professor Huxley's suggestion that 

 geographical provinces and zones may have been as distinctly marked 

 in the Pahuozoic 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 geograph- 

 ical 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 warmer and n)ore 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 inte- 

 rior heat of the earth. The Glacial period was an interrui)tion of the 

 continuity of its gradual cooling. In ])eriods of overflow, when the 

 land lay low and the sea had great extension under high latitudes, warm 

 marine currents had much (Uisier access to the poles than during conti- 

 nental periods. As we now know most about the deposits formed dur- 

 ing 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 



