290 H. L. FAIRCHILD POST-GLACIAL SUBMERGENCE OF LONG ISLAND 



"Among the most extensive and important clay formations occurring in 

 New Yorlv are those of the Hudson Valley. Here are deposits of two types : 

 (1) Estuary deposits of fine stratified sand, yellow and blue clay, and (2) 

 cross-bedded delta deposits, the materials of which are much coarser. The 

 estuary deposits indicate a period of depression and deposition in quiet water. 

 The clay is chiefly blue, but where the overlying sand is wanting or is of 

 slight thickness it is weathered to yellow, this weathering often extending to 

 a depth of 15 feet below the surface, and to a still greater depth along the 

 line of fissures through which the waters can percolate. The depth of oxida- 

 tion is of course influenced by the nature of the clay, the upper portion weath- 

 ering easily on account of its more sandy nature and hence looser texture. 

 Horizontal stratification is marked and the layers of clay are separated by 

 extremely thin laminjp of sand. At some localities the layers of the clay are 

 very thin and alternate with equally thin layers of sandy clay. This condi- 

 tion is found at Haverstraw, Croton, Dutchess Junction, Stonypoint, Fishkill, 

 Cornwall, New Windsor, Catskill, and Port Ewen, At all of the above men- 

 tioned localities except the last two the clay is overlain by the delta deposits 

 of rivers tributary to the Hudson, and the alternation of layers may be due to 

 variations in the flow of the rivers emptying at those points, the sandy layers 

 being deposited during periods of floods. . . . Isolated ice-scratched boulders 

 are not uncommonly found in the clay. 



". . . Of the blue and the yellow clay the former is the more plastic, but 

 both effervesce readily with acid, due to the presence of 3 per cent to 6 per 

 cent of carbonate of lime and are therefore, properly speaking, marly clays." 



In his detailed description of the clay banks, Eies makes frequent men- 

 tion of glaciated boulders in the clay, some of them being several feet in 

 diameter. 



W. M. Davis, in 1892 (16), published an admirable description and 

 discussion of Catskill delta features built in the Hudson estuary, clearly 

 recognizing that the '^Champlain submergence" involved the Hudson 

 Valley. He found the amount of submergence, as registered by the 

 cobble deltas in the Catskill Valley in the district of South Cairo, to be 

 270 to 280 feet. Our figure for the theoretic marine plain, as shoAvn in 

 plate 10, is 270 to 275 feet. And it may be noted, as added confirmation 

 of these figures, that nine miles eastward, across the Hudson Valley, is a 

 splendid gravel bar, a mile south of Hudson City, on the same isobase as 

 the deltas described by Davis, with altitude approximately 275 feet. 



Baron Gerard de Geer puldished, in 1892 (17), the results of his 

 reconnaissance work in eastern America bearing on Pleistocene changes 

 of level. Failing to discover distinct beach phenomena and not recog- 

 nizing the equal importance of postglacial deposits in the valleys, he 

 concluded that the submergence was very slight along the coast, and drew 

 his isobase of zero at 'New York City and northeast through Connecticut 

 and Massachusetts (plate 13, facing page 461). 



