GLACIO-AQUEOUS ACTION IN NORTH AMERICA. 187 



I do not mean to assert in the preceding inferences, that the 

 drift has taken a southerly du'ection from the very pole. In ad- 

 vancing northerly through Canada, the point may yet be reached, 

 as perhaps it has been in northern Europe, where this direction 

 ■udll be found' reversed. Still the great height at which the sur- 

 face has been eroded on the White INIountains, makes it proba- 

 ble that such a point, or axis of dispersion, if it exist, must lie 

 very far to the north ; certainly if, as analogous examples would 

 lead us to suppose, that axis be more elevated than any other 

 regions over which drift has been carried. No such lofty moun- 

 tains, I believe, have yet been discovered in the northern part 

 of this continent. They certainly must lie north of Hudson's 

 Bay, if they exist. 



4. Valleys of Erosion. 



It has always been a difficult matter to determine what vaUeys 

 have been due wholly or in part to glacio-aqueous agency. A 

 single example of this kind must stand instar omnium. Indeed 

 I have never met with another w^ell marked case in om- country. 

 The case refen'ed to, is upon Mounts Holyoke and Tom, in the 

 valley of Connecticut river. These mountains constitute about 

 fifteen miles of the northern extremity of a narrow trap ridge, 

 commencing at New- Haven and extending to Belchertown. All 

 that part east of Connecticut river is called Holyoke, while Tom 

 lies on the other side. The highest points rise above the river, 

 bet\veen eight hundred and a thousand feet, and the western and 

 northern side is very precipitous, except near the bottom, where 

 the sandstone crops out beneath the trap. The ridge lies in a 

 curvilinear du-ection, between the towns of East Hampton and 

 Northampton, Hadley and South Hadley, Amherst and Granby, 

 as shown on PI. VIII, f. 6, in such a manner that several miles of 

 its eastern part runs nearly east and west ; but its southern part, 

 nearly north and south. Its top is usually only a few rods wide ; 

 and on its southern and eastern side, it slopes rather gradually. 



Now as one approaches this ridge from the north, say through 

 Amherst, he will see its top to be irregularly serrated, as shown 

 on Plate VI, of my final Report on the Geology of Massachusetts. 



