76 Reviews — Br. Croll's Life and Work. 



on the subject. It follows, therefore, that the valleys of Scotland 

 and the north of England must at one time have been gorged with 

 ice, and thus many of Croll's postulates are undoubtedly true. But 

 his was a vivid imagination, and the perfervidum ingenium of his race 

 transported him, possibly beyond the bounds of probability, in the 

 tremendous expansion which he gave to the glaciation of these 

 islands generally. Moreover, there is reason for supposing that, 

 even subsequently to the publication of " Climate and Time," he was 

 a believer in a general Arctic ice-cap (see Geological Magazine, 

 1878, p. 396) ; whereas it is pretty clear, from the experiences of 

 Nordenskiold and other eminent scientific travellers, that glaciation, 

 as developed in the northern hemisphere, is a local phenomenon 

 dependent on the existence of mountain ranges, or at least of 

 elevated tracts of land. In the Arctic Ocean itself such an island 

 as Kolguev, for instance, has received its glacial debris from the high 

 lands to the southwards, and not in any sense from the direction of 

 the North Pole. 



In other respects also Croll's geological ideas were of an eminently 

 speculative character. He marshals an imposing array of figures, as 

 usual, to account for the Great Submergence, which many students 

 of glacial phenomena in these islands regard with considerable 

 doubt, beyond the moderate depression which is indicated by the 

 raised shell-beaches. Indeed, the more advanced glacialists of the 

 present day rather affect to look down upon a " submerger " ; whilst 

 some express strong doubts as to the occurrence of Interglacial 

 periods. 



But the most awkward circumstance in the geological aspect of 

 Croll's astronomical theory remains yet to be stated. If that theory 

 is sound, there must have been, throughout the Earth's history, 

 a constant recurrence of Glacial epochs. Admitting that consider- 

 able climatic changes have been effected, from time to time, by the 

 deflection of ocean currents and the uprise of mountain ranges, is 

 there any evidence, geologically speaking, of the regular recurrence 

 of Glacial periods, as required by the astronomical hypothesis ? 

 The geological record is so meagre on this score that CroU felt it 

 necessary to dwell with considerable emphasis on the " misconcep- 

 tions regarding the evidence of former Glacial periods," arguing 

 that the traces of glaciation are principally to be found on land- 

 surfaces, and that the transference of a land-surface into a sea-bottom 

 would probably obliterate every trace of glaciation. We know that 

 Croll believed in two great epochs of glaciation in Tertiary times, 

 the one in the Eocene and the other in the Miocene period. These 

 he supposed to coi'respond to certain periods of excessive excentricity, 

 as indicated in his famous diagram. The evidence is confined to 

 regions within the range of Alpine influences, and is perhaps of 

 about as much value in proving the existence of a " Glacial epoch " 

 as the occurrence of a few granite boulders in the Chalk. 



The most certain evidences of glaciation previous to the Pleisto- 

 cene Ice Age are to be found in the southern hemisphere, although 

 even these proofs do not of necessity imply a " Glacial epoch." 



