the Hudson and its Tributaries. 303 



Others bare been impressed with the possibilities of sub- 

 marine erosion bj a current along the sea-bottom, and have 

 sought in this way to avoid the necessity of assuming an im- 

 probable elevation . * 



The submarine channel is first and somewhat faintly discern- 

 ible about 5 miles off Sandy Hook. From this point north it 

 is submerged in later sediments and is unrecognizable. From 

 Princes Bay on the Staten Island shore outward the strata are 

 the soft and incoherent beds of the Mesozoic and Tertiary, but 

 from Princes Bay northward to Cornwall-on-Hudson the hard 

 metamorphic and plutonic rocks form the bottom ; still farther 

 north are the scarcely less resistant slates, sandstones, and lime- 

 stones of the Ordovician and Cambrian. In these two portions 

 erosion must have proceeded more slowly. 



Turning from the pre-G-lacial Hudson for the moment, the 

 post-Glacial work may be briefly reviewed in order to make 

 clear the state of our knowledge from this point of view. Upon 

 the later deposits much the most detailed work has been done. 

 It was early recognized that a period of subsidence had followed 

 the retreat of the ice sheet, making of the valley a quiet estuary 

 in which the fine Cham plain clays were laid down. Upon 

 these and after an uplift the very prominent gravel and sand 

 deltas were built up. Subsequent elevation brought about 

 their bisection and the exposure of the clays well above tide- 

 level. F. J. H. Merrill has traced these and their relations 

 from Xew York to Albany. f 



The local details of terraces, deltas, moraines, etc. have been 

 elaborated in still greater detail by C. E. PeetJ of the Depart- 

 ment of Geology at the University of Chicago, and by J. B. 

 "Wood worth § under the auspices of the 1ST. Y. State Geological 

 Survey. Both these writers treat the interesting question of 

 the old relations of Lake Cham plain and the Hudson, but these 

 later problems do not bear very closely on the points here to be 

 elaborated. These concern the drainage relations in that crit- 

 ical stage when the Glacial epoch was approaching, and they 

 give us some insight into the attitude of land and sea during 

 this and later time. 



The data utilized in this paper were gathered by the Board 

 of Water Supply of the City of New York and in connection 



* This alternative is briefly discussed with citations in J. B. Woodwortlrs 

 Ancient Water Levels of the Champlain and Hudson Valleys, Bull. 84, N. Y. 

 State Museum, 71-72, 1905. 



\ Post-Glacial History of the Hudson Eiver Valley, this Journal, xli, 460, 

 1891. Origin of the Gorge of the Hudson River, Bull. Geol. Soc. Amer., x, 

 498, 1899. 



% Glacial and Post-Glacial History of the Hudson and Champlain Valleys, 

 Jour. Geol., xii, 413-469, 617-660, 1904. 



?■ Ancient Water Levels of the Champlain and Hudson Valleys, Bull. 84, 

 N. Y. State Museum, 1905. 



