A, C. Lane — White Mountain Physiography. 353 



these, if they exist, is no matter of a week's glance, for 

 they are obscured by the ^ levels of glacial outwash 

 deposition studied by Fairchild. 



The series of late Tertiary and early Pleistocene 

 elevations, coupled with climatic changes, brought on the 

 ice age and the enswathement by an ice cap. The 

 tendency of an ice cap 10,000 feet thick extending from 

 Labrador, that is, with a radius of 9°, would be by gravity 

 to draw the water to it, so that if stagnant and full of 

 crevasses connecting with the sea, the sea-level would be 

 395 feet higher at the center, and 240 feet at the margin,^ 

 than were there no ice there. If we found no sea-level 

 next the old ice front as high as this above the present 

 sea-level, it might well be taken to indicate depression of 

 the White Mountain region since the ice left it. On the 

 other hand, if we suppose a certain amount of compres- 

 sion and isostatic adjustment of the crust under the ice 

 load, and that readjustment took place as the ice melted, 

 it is easy to account for any signs of depression and 

 elevation of the sea-level up to one third of the thickness 

 of the assumed ice sheet. If, then, we suppose an ice 

 sheet up to the level of the Boott Spur, say 5300 feet 

 5% A. T., it would have a thickness above the present 

 surface of some 2700 feet, and could account for a deep 

 sea-level in its crevasses and in front of it some 900 feet 

 above the present sea-level. This would be the lower 

 limit of the earliest and widest post-glacial valley erosion, 

 the limit up to which esker delta levels would build, and 

 toward which valley train deposits should be abundant. 

 It is, I think, the level followed by Fairchild, and given by 

 him as 725 feet A. T. at Bartletts on the Saco River, 800 

 feet at Goshen on the Androscoggin. Barrell has two 

 Pliocene terraces, the ^'Prospecf at 940 feet, and the 

 ^^Towantic'' at 740 feet, that may easily blend with it in 

 broad landscape views, but should pass under the glacial 

 deposits, not over, and would be likely to have a different 

 tilt. 



It must not be forgotten that here, as in Michigan, a 

 plane connecting the various marine levels close to the 

 ice front at different stages of the ice front by no means 

 represents the water level at any one time. The 

 disturbing effect of the ice on the water-level retired with 

 the ice front, in part simultaneously, in part shortly after, 



* Using Woodward's formula 64 and 67 of Bull. 48, with p = 9°. 



