I 



ANCIENT WATER LEVELS OF CHAMPLAIN-HUDSON VALLEYS 189 



not be taken as a criterion of the presence of the glacier unless in- 

 dependent evidence of the presence of the ice be found and even 

 in this case the direction of the overthrnsting movement shown by 

 the clays should agree with the axis of movement of the ice margin. 

 As this movement in the clays would be away from the ice contact 

 terrace it should be possible to discriminate in favorable situa- 

 tions contortion through gravitative sliding from contortion by ice 

 thrust. In the Croton point case, there is evidence of the presence 

 of the ice in the morainal revetment of the remaining portion of 

 the old ice contact terrace on the north and the contortions have 



Fig-. 23 Contortion and intrusion of clays in sand bank south of Port Kent railroad 

 station, as seen July 31. 1900: A, the clay ; B, the foresei sands of the delta ; C, upper uost 

 undisturbed sand layers 



their axial planes thrown over to the south away from the ice, 

 hence it is possible to infer that a slight ice thrust is indicated 

 here. 



The case is described elsewhere in this report in which the ice 

 sheet has overrun clays in the Hudson gorge between Schuylerville 

 and Fort Edward, producing contortions of large size. 



At many points where streams have constructed deltas on the 

 margins of the clay area crumpling is to be suspected as an effect 

 of the weight of the overlying sand and gravel. A rather marked 

 case, probably a locality earlier observed by Ebenezer Emmons, is 

 that of the southernmost lobe of the marine delta of the Ausable 

 exposed in a section south of the railroad station at Port Kent on 

 Lake Champjain. The sands which have here been deposited over 

 the clays have resulted in the disruption of the latter in the man- 

 ner of irregular dikes penetrating the overlying sands. 



