GLACIAL EROSION ASD TRANSPORTATION. 240 



in Little Valley, Cattaraugus county, N. Y. ; unless we sup- 

 pose that all the Canadian bowlders were borne upon the sur- 

 face of the ice, which is clearly impossible. 



Bowlders of Alpine glaciers seem always to descend to their 

 final resting-place, but we have innumerable proofs that the 

 American ice-sheet managed, in some way, to carry bowlders 

 from valleys up to mountain- tops, although the amount of 

 elevation in many cases, if not in all cases, may be much less 

 than we are inclined, on a first inspection of the facts, to take 

 for granted. 



In the case of the Helderberg limestone bowlders men- 

 tioned, found, by Mr. Lew r is on the crest of the Kittatinny 

 Mountain, it is not necessary to suppose that it came from 

 Godfrey's Ridge, only three miles distant (north) in the valley 

 below, 1,000 feet beneath its present position. Indeed, the 

 direction of the scratches on the mountain-side make such a 

 supposition incredible. It is plain that it must have traveled 

 down the valley of the Delaware, and may have come from the 

 continuation of the range in the State of New York. The 

 elevation of the surface gradually increases going east. The 

 rise in the bed of the river for the first thirty-five miles, from 

 the Delaware Water-Gap to Port Jervis, is about 200 feet. 

 The rise from Port Jervis to the Roudout-Walkill divide, 

 twenty miles, is 80 feet more. There the crest of the Helder- 

 berg Ridge must be nearly 1,000 feet above tide. The crest of 

 the Kittatinny Mountain where the block lies is about 1.500 

 feet above tide. Therefore, if the block came these sixty-five 

 miles, it has been carried up only 500 feet above its original 

 situation. 



Still, it remains a problem by what sort of internal move- 

 ment a stone held in the ice can ascend, however gentle may 

 be the gradient upward. That internal movements take place 

 in all glaciers, is made visible to the spectator by their spoon- 

 shaped stratification, and by the different rates at which their 

 upper, lower, middle, and lateral parts move along, as well as 

 by the fact that they press forward over rock-barriers. But 

 -o general a statement has no scientific value when evoked to 

 explain the actual translation of a bowlder up a mountain- 

 slope. In fact, our knowledge of how such an operation was 



