TIIK POST-PLIOCENE. 21 



fore no geological necessity to appeal to the varying eccentricity of 

 the earth's orbit and the precession of the equinoxes, or to an imagined 

 change of the earth's axis of rotation, or of the obliquity of the 

 ecliptic, or of the energy of the sun's radiation. If these, or any of 

 them, can be proved on other grounds, geologists may fairly be called 

 on to allow for their influence ; but there is no geological necessity for 

 them, other than the exigencies of an imaginary period or succession 

 of periods of continental glaciation, of ■which unquestionably there is 

 no geological evidence in Eastern America. For facts in siqiport of 

 this view, I may refer not only to the chapter on Acadian Geology on 

 this subject, but to my subsequently published Notes on the I'ost- 

 ])liocene of Canada. It Avould occupy too much space to repeat 

 them here, except in so far as they may come up under subsequent 

 heads. 



Boulder Clay and Glacial Erosion. — From the views as to these 

 subjects, given fully in Chapter V., I have seen as yet no cause to 

 recede. Since they were published, the doctrine of continental 

 glaciers has waxed and waned, and the greater number of the ablest 

 workers in this field are now not very remote from the position 

 which I occupied in 1868. Quite recently, the discovery by the 

 "Challenger" soundings that a deposit of stones and mud is now rapidly 

 forming in the Soutli Pacific by the melting of ice, the observations 

 on the action of pack ice by the recent Arctic Expedition, and the ex- 

 position of the action of pick ice on the coast of Newfoundland, given 

 by I'rofessor Milne in the Geological Magazine for 187(3, have 

 strengthened very much the position of those who hold that the glacial 

 drift and striation have been mainly due to floating sheets and bergs, 

 at a time when the northern seas were much more extensively occu- 

 pied with them than at present.* I have very fnlly discussed this 

 subject in my Notes on the Post-pliocene Geology of Canada, 

 already referred to, and shall merely quote here a passage on a subject 

 referred to in Chapter V., and on which more complete information 

 has since been obtained. I refer to the erosion of the basins of the 

 great American lakes : — 



" These have been cut out of tlic softer members of the Silurian 

 and Devonian formations ; but the mode of this excavation has been 

 regarded as very mysterious; and, like other mysteries, has been 

 referred to glaciers. Its real cause was obviously the flowing of cold 

 currents over the American land during its submergence. The lake- 

 basins are thus of the same nature with the deep hollows intervening 



* See also Professor Iliiurs iniiier in tlic Canadian Naturalist, 1S77, referred to 

 further on. 



