MUSEUM OF COMrAKATIVE ZOOLOGY. 215 



granite in the conrse of the trail, which is just at the foot of the pres- 

 ent terminus of the Southwest Slide. At both localities the rock is of 

 the coarse gray variety that is exposed at the third and fourth falls, 

 and is destitute of glacial markings. The surface is honeycombed by 

 decay, which, at the lower station, has gone so far that it was there 

 impossible to break out, with a heavy hammer, specimens which at all 

 approached a sound condition. 



The only rock in place to be seen upon the Southwest Slide occurs 

 two thirds the way up from its foot, at an elevation of about 3,500 

 feet. It is a fine-grained, dark gray granite, approaching in appearance 

 some of the inclusions that are found in the basin, and well adapted to 

 resist decomposition. It lies, as at the stations below, in concentric 

 sheets,* which have here an inclination of about 30°, and is smooth, 

 hard, and free from all indications of decay ; but not a scratch or 

 other sign of glaciation appears upon it. It is a small area, only sev- 

 enty-five feet along the slope, and perhaps a third as wide, and dis- 

 appears above, below, and at the sides, under the debris of the slide, 

 beyond the slanting face of which the ledge scarcely projects. If it was 

 first uncovered, in recent times, by the descent of the avalanche of 1816, 

 as from the surroundings seems not improbable, the absence here of 

 grooves and striae is significant as respects the glaciation of the higher 

 parts of the mountain. 



If evidence of glaciation upon the summits of Ktaadn exists, it must 

 be other than that to be derived from smoothed and striated surfaces. 

 It will be maintained by many that such evidence is supplied by the 

 flat tops of the Table Land, and of several of the spurs, and by the well- 

 rounded northern summits and faces. To this it may be objected that 

 table-topped mountains are not wanting in regions where neither drift 

 nor other indications of glaciation have been recognized. The state- 

 ment, however, is open to the rejoinder that, in such cases, the shape 

 may be rationally accounted for by obvious peculiarities of structure, as 

 is the typical instance of Table Mountain, near the Cape of Good Hope, 

 which is a mass of granite capped by horizontal beds of sandstone. 

 The prevalence of steep fiices upon the sides of Ktaadn, as already re- 



* My observation of Elaine granites in general, and esjiecially at Mt. Ktaadn, 

 forces me to the conclusion that the concentric lamination of granite is due to causes 

 connected with the original structure of the rock, and not, as has been maintained 

 by Professors Shaler and Hunt, to superficial variations of temjierature during the 

 changes of tlie seasons. It would seem, then, to be putting terms in their logical 

 order to speak of the conformity of present surfaces to the inclination of the granite 

 sheets, rather than of the lamination as conformable with superficial features. 



