MUSEUxM OF COMPARATIVE ZOOLOGY. -35 



It seems possible to arrive at a satisfactory explanation of the origin 

 of the trains by first considering the principal train, which is, of all the 

 four, the most complete, and the one whicii -reveals most nnmistakubly 

 its origin. Fry's Hill, evidently the point of origin of this train, has 

 been referred to as a sharp knob, situated on the crest of the range, and 

 composed chiefly of chloritic schist. To the north and south of this 

 knob, however, exposures of chloritic schist are wanting, the rock being 

 chloritic sandstone and mica schist. It seems tolerably plain, then, that 

 it is partly to the sharpness of the knob, and partly to the narrowness 

 of the limits to which the chloritic schist is confined, that the narrow 

 distinct train owes its formation. 



The second train is, in all essential characters, like the principal train. 

 Its direction in the Shaker Valley indicates that it originated upon a 

 knoll situated on the crest of the range, half a mile S. S. W. from the 

 origin of the principal train. It would be natural to expect to find that 

 the train is continuous to this point, and that the knoll is composed, 

 like Fry's Hill, of chloritic schist. On the contrary, it is composed of 

 chloritic sandstone, and no chloritic schist boulders are to be found on 

 its eastern slope. The explanation seems to be that the knoll once bore 

 a mass of chloritic schist similar to that upon Fry's Hill, though much 

 less in amount, and that, though it continued for a time to give off 

 boulder material, the supply of chloritic schist in that spot was finally 

 exhausted, the fragments having been all torn from the knoD, and at 

 length deposited in their present positions. 



In a similar manner the origin of the third and minor trains may be 

 accounted for. 



In what particular manner were the boulders transported by the ice- 

 sheet 1 They either rested on its upper surface, or were dragged along 

 between its lower surfiice and the bed-rock, or were imbedded in the 

 mass of the ice. 



The first of these suppositions cannot be sustained, since it presup- 

 poses clifts upon the Canaan and Lebanon Kange which reached above 

 the surface of the ice, whereas an ice-sheet which could move across val- 

 leys six hundred feet deep, without being materially deflected from its 

 course, must have covered the highest land in the region to the depth 

 of many hundred feet. 



The second supposition is equally invalid, since, if these boulders had 

 been dragged along under the ice, they would of necessity be much 

 abraded, most of them showing smoothed surfaces, which would be likely 

 to bear striae. None of these eftccts are to be found upon them, how- 



