188 



NEW YORK STATE MUSEUM 



in the Hudson valley. Still there are narrow tracts bordering the 

 river bank as at Newburg where inconsiderable slips might cause 

 much damage or loss of life. The confinement of the river within 

 its rock gorge is a further protection to the masses of clay which 

 remain on the borders of the river. 



Landslips in a glaciated district particularly where clays are 

 covered with gravels and sand or glacial till often simulate the 

 irregular topography peculiar to undisturbed glacial deposits. 

 Even the structure of glacial deposits may in some cases simulate 

 broad landslip movements for the reason that under the pressure 

 of overriding ice the subjacent loosely textured deposits have been 

 disturbed in much the same way as in normal landslips; but the 

 association of glacial features such as the indications of the 

 former front of the ice sheet and the distribution of the deposits 

 usually make it possible to discriminate landslip topography from 

 glacial topography. 



Contorted clays. Contorted clays have long attracted the at- 

 tention of observers in the Hudson and Champlain valleys. Eben- 

 ezer Emmons 1 noted contortions in the clays at Albany and as 

 early as 1S46 referred the phenomenon to the sliding of upper 

 beds over lower ones in the movement of the clay bank toward 

 its unsupported edge. This explanation appears to be satisfac- 

 tory for many cases in the clays laid down after the final disap- 

 pearance of the ice sheet from the district. It finds confirmation 

 in the numerous instances of the sliding of masses of clays or 

 landslips which have been observed at one point or another along 

 the banks of the Hudson. 2 The contortions can only indicate the 

 beginning of a restrained movement of this nature. But there 

 are other ways in which contortions may have arisen in this field, 

 viz, through the advance of the ice sheet on the clays laid down 

 about margins of the ice, and through the lateral flow of clays 

 from the growth of superposed deltas of sands and gravels about 

 the margin of the clay tracts, a cause of contortion in clays noted 

 by Russell 3 in the dessicated Lake Lahontan of the Great Basin. 



Contortion through the forward push of the ice along its margin 

 is to be suspected in the case of the contorted clays in the basal 

 portion of the section on Croton point; but the contortions can 



^mirioDS, E. 1847. See bibliography, 53. 

 2 Dwight, W. B. 188G. See bibliography 45. 



3 Russell, I. C. Lakes of North America. Boston 1895. p.50, fig. 7. 



