GLACIAL DRIFT. 325 



winters than summers, induced by precession of the equinoxes, with a 

 period of great eccentricity of the earth's orbit. This might have been 

 cited as a fourth theory of glacial cold, and has been abundantly pre- 

 sented earlier in the volume, page 5, ct scq. The coincidence of these 

 astronomical and physical conditions would be fully adequate to produce 

 the intense cold. 3. Some authors add the existence of conditions 

 favorable to the abundant precipitation of moisture in northern regions. 

 Certain collateral conditions seem to have been connected with these, as, 

 4. The greatest accumulation of frozen moisture seems to have been 

 about Labrador and Hudson's bay, whence it pushed outwardly in all 

 directions, but mainly southerly, because that was the direction of least 

 resistance. 5. The accumulation of several miles thickness of ice seem 

 necessary in order to understand how motion could be induced. The 

 land about Labrador is not so high as the mountains of New Hampshire, 

 and we cannot reasonably assume such an enormous elevation of it as 

 would be required to cause the flow over New England, or to the plains 

 of Dakota. 6. The adoption of Croll's Molecular theory of ice-motion, 

 or something similar to it, seems necessary. 7. The New England 

 south-east movement probably resulted from the overflow of the St. 

 Lawrence basin. The ice must have accumulated sufficiently to over- 

 flow the St. Lawrence-Connecticut water-shed before it could have 

 moved over the White Mountains. 8. How extensive the earlier south- 

 west movement over much of New England may have been is not yet 

 determined. Only scanty traces of it remain. 



Inter-Glacial Deposits. 



Messrs. Geikie and Croll insist upon the existence of warm periods in 

 the midst of the long glacial winter sufficient entirely to melt the ice, 

 and give rise to a succession of cold eons, alternating with the warm 

 ones. Mr. Upham has already referred to the untenability of this posi- 

 tion, page 7, and has described phenomena similar to those called inter- 

 glacial by the Scotch authors (pp. 108, 131-137, 163, 164, 176, 290). It 

 seems very clear that there are no phenomena in New Hampshire re- 

 quiring us to accept the view of a succession of ice-periods. When the 

 ice had once formed, it must have continued to rest upon the land 

 VOL. III. 42 



