cviii GENERAL SUMMARY OF SCIENTIFIC AND 



feet. Over the latter two are abundant deposits of unstrati- 

 fied drift, which in the middle plateau is almost wholly from 

 the crystalline rocks of the eastern range or Laurentian axis 

 and the limestones adjacent, while on the higher western 

 plateau, though boulders from the latter region still abound, 

 more than one half the drift is from the Rocky Mountains. 

 These themselves afford abundant evidence of glaciers. The 

 author conceives that sub -aerial denudation had already 

 given to the region nearly its present surface before the gla- 

 cial period. He concludes that the phenomena of the drift 

 in these regions do not require to account for them a polar 

 ice-cap, but are to be explained by the action of local gla- 

 ciers from the Laurentian axis drifted westward across the 

 submerged prairies toward the Rocky Mountains. 



In England the nature and causes of the drift formation 

 have been much discussed. The intercalation of stratified 

 deposits in the unstratified drift, and the presence in both of 

 marine remains, apparently indicate for a part, if not the 

 whole, a submarine origin. In order to conciliate these facts 

 with the hypothesis of a great ice-sheet, Mr. Goodchild has 

 attempted to show that none of the phenomena prove the 

 former agency of the sea, but that all these deposits were 

 formed under land-ice, and in part by the agency of sub-gla- 

 cial streams, the ice -sheet having excavated from their 

 ocean-bed and pushed up on the land the marine deposits in 

 its onward march. There is, however, a strong reaction from 

 this hypothesis in England [Record, 1874, p. Ixxiv.], and sev- 

 eral of Goodchild's colleagues in the Geological Survey of the 

 United Kingdom have opposed him in recent papers, notably 

 Hardman, Dakins, and Ward. The latter observes, " The 

 difficulties involved in the theories of Croll, Belt, Goodchild, 

 and others of the same extreme school, certainly press upon 

 me and I think I may say also upon others of my colleagues 

 increasingly as the country becomes more and more famil- 

 iar in its features." He suggests, from the observations of 

 late arctic voyages, that prevailing winds acting upon the 

 surface-ice, rather than currents, are to be taken into account 

 in considering the distribution of drift boulders, and quotes 

 the lano-ua2;e of Sedgwick in 1842, who, referrino- to the 

 transport of granite blocks from the hills of Cumberland to 

 the shores of the German Ocean, says, "No one, I trust, will 



