222 



BULLETIN OF 'IllE 



its progress it has successively prostrated, buried, and passed over the 

 opposing small trees, in no case, at the intermediate part which we saw, 

 carrying away the trunks or branches. 



Certain huge blocks of granite that lie on the floor of the South 

 Basin have been regarded by some as erratics, but m fact arc parts of 

 the adjacent cliffs, and owe their present location indirectly to the 

 agency of ice. They arc fragments of the eastern wall, which, falling 

 upon inclined planes of compacted snow or ice accumulated in winter 

 agahist the basin sides, have slid or rolled several rods beyond the 

 great talus, 350 feet in height. Lying so far beyond the talus, which is 

 the receptacle of most descending fragments, they have been mistaken 

 for erratics, notwithstanding their agreement in composition with the 

 nearest cliffs. In the same way alone can we account for the presence 

 of great rock masses at stations so far out from the northern foot of Pa- 

 mela that they cannot be supposed to have rolled thither over any other 

 surface than an inclined plane of ice. Here, too, somewhat west from 

 where the foot of the cleared strip must be, are four approximately par- 

 allel ridges made up of granite blocks of all sizes. They are of consider- 

 able length, and have between them hollows fifteen or twenty feet deep 

 and some rods wide, but of unequal width. They appear too recent, — 

 resembling parallel tali of fresh material, — and too near together, to 

 correspond to my notion of old terminal moraines ; and I was unable 

 to explain their origin in any way satisfactory to myself. 



A change that was produced in a part of the southern lobe of South 

 Basin, dining the early summer of last year, is instructive, as illustrating 

 the origin of the Ktaadn slides. The gorge between the Chimney and 

 the peak of Pamela — a ty])ical instance of erosion — is a deep and nar- 

 row cut, forty feet wide at its head, diminishing to ten at the foot, and 

 upon its floor to two or three feet at the outlet, where it is a polished, con- 

 cave water-course worn in the solid rock. Its small drainage area, and 

 evidence derived from the accumulations about its foot, show that even 

 in times of flood it ordinarily carries a stream of but moderate size. In 

 ■the summer of 1879 the debris that had been brought down in a series 

 of years extended downward from the foot in the usual fan-shaped " cone 



ahovo. The hillside from the upper terraee to the top is 1,300 feet in length. The 

 inelination of the street near the summit is 11" ; midway, 7^ ; below, IVom d" down 

 to 0". Early in the winter of 1878-79, the snow, after continued rain, aysumed the 

 slushy state, and, starting from the middle of the hill, whore tlie inclination is only 

 7''y rushed suddenly down the street with a roar, and piled itself on the level ground 

 at the foot. On the steeper upper half tlje snow lay unmoved. In the ninety years 

 since the street was opened, tliis is the only ease of the kind recorded. 



