CLACI.W. PHENOMENA. 



65 



causes ample, means for accounting for tin- whole of the appearani 

 including the travelled blocks and the scratched and polished rock- 

 surfaees. This, however, is only a general explanation. Had we 

 time to follow it into details, many most interesting and compli- 

 cated facts and processes would be discovered. J mention merely one 

 for an example, as it illustrates the manner in which the land may 

 have subsided beneath the boulder-bearing seas. I have stated that 

 large blocks of sandstone from the plains of Cumberland have been 

 carried to the summits of the Cobequid Mountains. When these 

 blocks were carried to their present place, the waters must have 

 reached to the summits of the hills; but at that time tlic plain from 

 which these blocks came must have been several hundred feet below 

 the seadevcl. How then could ice take them from such a depth? 

 We may fancy huge icebergs grounding in this deep water, but they 

 could not float over the hills or ground against their summits. The 

 explanation is that the country was gradually subsiding. While the 

 water was shallow, the blocks were drifted against the base of the hills. 

 As the land sunk, the ice-fields of successive years gradually pushed 

 them higher, until the summits of the hills were submerged so deeply 

 that the ice could no longer take up the blocks. Most of the ap- 

 parent anomalies of the drift may be explained in such ways, when 

 the theory of ice-carriage is once admitted. 



I have retained the above explanation of the boulder clay, which 

 appeared in my edition of 1855, because I have as yet seen no reason 

 to change my opinion on the subject, although I have since that time 

 had opportunities of studying the Post-pliocene of ( ianada and other 

 parts of America and of Europe, and have read nearly all that has 

 been written by the advocates of a terrestrial origin of this deposit, in 

 a supposed glacial period when the whole of the northern parts of 

 Europe and America are imagined to have been covered with glaciers, 

 or rather with a universal glacier like that of Greenland, but on an 

 enormously larger scale. The more I have considered this hypothesis, 

 the more improbable it has appeared, whether in a mechanical, me- 

 teorological, or geological point of view ; and a recent visit to Mont 

 Blanc, and the study of the effects produced by icebergs in the Straits 

 of Pelleisle, have more fully established in my mind the belief that 

 floating ice and the Arctic current have been the grand agents em- 

 ployed. As the glacier hypothesis of Agassiz, Ramsay, and others, has 

 been incorporated into the best American text-book of geology, that 

 of Professor Dana, and has recently been ably advocated in the case of 

 New Brunswick, I may here give some of my reasons for dissenting 

 from it, as stated in a paper published some time ago in Canada. 



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