SAYLES: THE SQUANTUM TILLITE. 149 



Atlantic, and that the same kind of argillaceous masses are found in 

 the tillite of Australia (Wilkinson, p. 194) and other places, and in 

 Pleistocene till, it is necessary to suppose — unless some better agency 

 can be advanced — that moving ice tore up all these shale or slate 

 fragments. A moving ice-sheet would tear up a clay-bed; part of 

 the torn up mass would be over-ridden and dragged up into the till, 

 and some of it would be seized by the glacial torrents and carried 

 forward and deposited somewhere in front of the ice. It seems per- 

 fectly possible that this latter method explains these lumps deposited 

 with the conglomerate. A large fragment would be rolled over along 

 the bottom more easily than a rock of corresponding size, on account 

 of the lower specific gravity of clay and lessened liability to wedging 

 on account of ready marcellation when moved against an obstacle. 

 In this way a large fragment might be moved for some distance and 

 when finally brought to rest would be much reduced in size.^ As for 

 the fragments at Atlantic, the ice-front could not have been very 

 far away, and a retreat must have follow^ed, for above this horizon a 

 slate bed is found. Another advance is indicated by another con- 

 glomerate bed with slate fragments and tillite. Above these beds 

 come about 25 feet of sandstone with fine conglomeratic layers, and 

 some shale or slate fragments, and in contact with this the main 

 body of the tillite. Knowing that moving ice does disrupt clay-beds, 

 and the proximity of the tillite to these shale or" slate fragment hori- 

 zons, this association makes it very probable that ice was the agency 

 responsible for the fragments. I am well aware that such fragments 

 may also be due to the undermining of clay-beds by streams, and 

 the falling in of clay fragments so undermined, but the evidence in 

 these cases under consideration points to ice-action. 



The tillite has a very ragged contact with this underlying sandstone, 

 as if the surface of that deposit had been disrupted by violent move- 

 ment such as that of ice. In places the tillite appears to have been 

 pushed down into the sandstone. The lower part has a fine argilla- 

 ceous matrix with here and there coarse patches. About ten feet 

 from the bottom the matrix is uniformly fine. Farther up in this 

 main tillite bed the matrix becomes coarser and at the point highest 

 up resembles very closely the tillite at Squantum Head. 



1 By experiment I have found that frozen clay disintegrates as soon as it comes 

 In contact witii water. The temperature of the water used was about .32° F. Plastic 

 clay in an unfrozen condition does not disintegrate with anytliing like the same 

 rapidity. It is inferred from this that the clay fragments under discussion were not 

 frozen. 



