154 bulletin: museum of compaeative zoology. 



is found a large mass of sandstone about 15 feet in diameter, the upper 

 part of which is stratified with layers of slate alternating with sand- 

 stone. It appears to have been a part of an underlying bed which had 

 been disrupted and dragged laterally upward into the till. The entire 

 mass is surrounded with tillite. This is by far the largest block 

 yet discovered in the tillite. In view of the fact that a bed of sand- 

 stone underlies the tillite at Atlantic, it is inferred that this sand- 

 stone mass is a part of a similar bed disrupted and included in the 

 tillite. That the lower transition-beds and the Roxbury conglom- 

 erate are present, but hidden from \'iew in this locality' is also inferred 

 from the large amount of fragments of the conglomerate found in the 

 drift on Squantum just where they should be found. The stone-walls 

 are made up chiefly of this variety of rock. The sizes of the pebbles 

 in the Roxbury drift fragments average the same as in the Roxbury at 

 Atlantic; lithological characters are the same. The texture of the 

 Roxbury conglomerate in different localities is extremely variable, 

 and hence to find the same texture in these fragments as at Atlantic, 

 on nearly the same strike and only a short distance away, would 

 indicate that they were not transported far but came from this vicin- 

 ity. The great preponderance of these Roxbury fragments over other 

 kinds of rock would also indicate a local origin. It is from this evi- 

 dence that I have felt justified in believing that the tillite here has 

 not been doubled, but is a bed shown in its actual thickness. 



Near the very top of the tillite there is a multitude of slate frag- 

 ments, which had their cleavage developed after inclusion in the tillite. 

 They have very irregular shapes, none of them being water worn, 

 and many of them bent and twisted as if they had been in a plastic 

 condition when the ice moved over the surface. It is evident that 

 here the ice plowed over a clay-bed, breaking it up and dragging the 

 clay fragments, thus disrupted, upward into the till. Some of these 

 fragments are large, one measuring four feet long by two feet wide in 

 the other dimension. Most of them are about a foot long. Shearing 

 has changed the original shapes in some cases. It is clear, however, 

 that the bending, twisting, and tearing observed in these cases has 

 not been brought about by shearing. S?e Plate 8. 



Dr. Ellsworth Huntington, who was with Dr. La Forge and myself 

 on our first visit to this locality, found a very remarkable case of 

 deformation in a slate bed. The bed in question is about three feet 

 thick. A part of this bed has been turned up so that it makes an 

 angle of about 90° with the original bedding for several feet, and about 

 ten feet farther on the bedding again assumes its original position. 

 There are two cases of this sort here not far apart. 



