12 J. W. Goldthwait — Glacial Cirques 



cock has proved, * it is worth while to consider whether the 

 gulfs may not have been shaped by the movement of the con- 

 tinental ice. Undoubtedly there are instances in the White 

 Mountains as elsewhere of valleys in which the ice sheet, chanc- 

 ing to move longitudinally, widened and straightened the pre- 

 glacial river valleys, converting them into U-shaped troughs. 

 The Crawford Notch and other notches may be examples of 

 this sort. These, however, are "through valleys," — deep sad- 

 dles which connect the lowland on one side of a range with the 

 lowland on the other side. The ravines around the Presiden- 

 tial Range, on the other hand, head boldly against the moun- 

 tains in semicircular cliffs. Consider, for instance, King 

 Ravine. It is hardly conceivable that the ice, pushing south- 

 eastward up King Ravine, would pluck blocks from its sides to 

 the extent indicated by the excessive breadth of the trough, 

 and at the same time, ascending its head, develop a cliff there 

 which is almost equally precipitous. Such a headwall, rising 

 twelve hundred feet at an angle of 45 or 50 degrees, would 

 offer too great resistance to ice movements to be itself the 

 product of regional glaciation. Other ravines, such as Hunt- 

 ington and Tuckerman Ravines, which, as just pointed out, 

 trend southeastward, head in crescentic precipices similar to 

 the headwall of King Ravine. Surely the ice which ascended 

 King Ravine and then, passing across the col between Mounts 

 Madison and John Quincy Adams, and descended into Madi- 

 son Ravine would not have carved the heads of these opposed 

 valleys in the same manner. It is equally improbable that the 

 immense trough of the Great Gulf should have been excavated 

 by the ice sheet, trending as it does almost perpendicular to the 

 ice movement. One can see, indeed, in the contrast between 

 the precipitous northwest side of the Great Gulf and the more 

 moderate southeast side indication that the gulf form antedates 

 the arrival of the ice sheet and has been somewhat modified by 

 the transverse regional glaciation. Finally, the most vital 

 objection to the ice sheet erosion theory of these ravines is 

 that one or two valleys, like that of Snyder Brook, retain their 

 narrow, crooked form, although they were in a position to 

 suffer exactly the same widening, deepening, and straightening 

 at the hands of the advancing ice as the neighboring ravines 

 might suffer. 



While thus the theory of abnormal jointing and frost action 

 and the theory of ice sheet erosion fail to explain the ravines 

 either singly or collectively, the remaining hypothesis — that of 

 local glaciation by valley glaciers — presents no such difficulties. 



*C. H. Hitchcock : Existence of glacial action upon the summit of Mount 

 Washington, N. H., Proc. Amer. Assoc. Adv. Sci., vol. xxiv, pp. 92-96, 

 1876. 



