Il8 NEW YORK STATE MUSEUM 



that in late Cretaceous and Tertiary time there was overlapping iar 

 inland on the eroded surface by sediments belonging to the late 

 Alesozoic periods. It is judged, for example, that the Hudson river 

 itself has found its way toward the sea nearly in the particular posi- 

 tion which it now occupies on such a sedimentary series of coastal 

 plain deposits. If this is true, it was probably at the close of Cre- 

 laceous time that the Hudson river found its way across this terri- 

 tory, and continued erosion developed a tendency to a new pene- 

 plain level in late Tertiary time. Not long enough time or enough 

 stability was maintained, however, to accomplish more than the 

 beginning of such a plane in the widening of valleys and the develop- 

 ment of flat bottom in accord with the new base level, while the 

 divides reached up near to the former earlier Cretaceous peneplain. 

 At one stage at least a rejuvenation of the streams was inaugurated 

 by a new elevation of the land and new trenches were cut into the 

 bottom of these valleys. This was accomplished prior to the glacial 

 period. It may be that this last step is more complicated than is 

 suggested by the above statement. One of the evidences of a 

 greater complexity is the occurrence of islands within the Hudson 

 river gorge. It is explained in connection with them that the gorge 

 was partly filled with new deposits, and then when the river was 

 rejuvenated enough to cut down into them, it found itself 

 entrenched in places along the side of the true former gorge in such 

 manner as to be impossible for it to escape and slip over into the old 

 position. It would necessarily thereafter develop a new gorge in 

 that position which would ultimately become a part of the final com- 

 pleted Hudson river gorge. If projecting ledges were cut off in this 

 manner on one side by the abnormally located river, and on the 

 other side by the old channel of the river belonging to a preceding 

 epoch, they would necessarily stand as islands in the gorge. It may 

 be that this is the history of them ; at least no better has yet been 

 proposed. 



During the late Tertiar}-, these physiographic details were pro- 

 duced and have become a part of the history of the region. The 

 development of surface features as now represented, is the last stage 

 in the history of the region and is regarded as the proper field of 

 physiography. These features, therefore, will be discussed further 

 under that head rather than at this point. 



Glacial history. The region was subjected to ice invasion in the 

 glacial period and seems to have been entirely covered with ice. 

 Glacial erosion is evident as well as glacial deposits. The result of 

 the glacial history has been in large part a subduing of the relief. 



