SUBMERGEXCE PHEXOMEXA 611 



initial marine level, but are, naturally, more evident in areas of abundant 

 detritus and at the lower levels. About Plymouth they are very strik- 

 ing, up to 120 feet. They are also conspicuous at Truro and Xorth 

 Truro up to the highest land surface, at 110 feet. 



6. PELL-MELL GRAVELS 



These deposits have already been discussed. They are accumulations 

 of detritus from glacial drainage poured into water too deep to allow 

 assorting and stratification, and are rather characteristic of the moraina] 

 belts. The sand and gravel, the fine and the coarse, are mingled closely, 

 and the deposits are compact, lacking the loose and open structure com- 

 mon to gravels of other districts. These gTavels are more abundant 

 toward the glacial border, perhaps chiefly because of the greater depth 

 of water, and were especially noted in southeastern Massachusetts and 

 in Barnstable County. 



Wave-work of the shallowing waters might sometimes spread a veneer 

 of assorted stuff, and on marginal slopes the shifted gravel might 

 resemble backset or foreset beds and help to give a resemblance to con- 

 structional outwash plains. 



7. SUPERFICIAL CLAYS 



The extensive deposits of clay, the surficial material over large areas 

 in eastern Massachusetts, are of necessity recognized as the product of 

 deep or quiet water. They are precisely the expected effect of far re- 

 moval of the ice-front, in deep water, before any large rise of the sea- 

 bottom. The age of these surface clays is the vital question. 



Writers admit that the clays of the Boston Basin were deposited In 

 deep water, open to the sea, and that their occurrence at the present 

 elevation of 100 feet over tide may not represent, on account of erosion, 

 the full original height (31, page 991). The water surface in which 

 the clays were laid must have been 100 to 200 feet over the clays, judg- 

 ing from the map of isobases. 



But the Pleistocene clays and the other records of submergence, as 

 the Highland Light, beds and the Sankaty fossiliferous sands, were 

 thought to have been deposited and elevated previous to the last ice- 

 invasion. Appeal is made to down-and-up movement of the land dur- 

 ing the life of the supposed earlier ice-sheets, and to elevated attitude of 

 the land during the last ice epoch. In other words, the land was low, 

 with submergence and clay deposition, during the time of removal of the 

 earlier ice-sheet, but was elevated while the last ice-sheet was imposed. 



