104 NEW YOEK STATE MUSEUM 



Among the most extensive and important clay formations 

 occurring in New York 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 weather- 

 ing 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 water can percolate. The depth of oxidation is of course influ- 

 enced by the nature of the clay ; the upper portion weathering 

 easily on account of its more sandy nature and hence looser text- 

 ure. Horizontal stratification is usually present and the layers 

 of clay are separated by extremely thin laminae of sand. At 

 some localities the layers of the clay are very thin and alter- 

 nate with equally thin layers of sandy clay. This condition 

 is found at Haverstraw, Croton. Dutchess Junction, Stony Point, 

 Fishkill, Cornwall, l^ew Windsor, Catskill and Port Ewen. 

 At all of the above-mentioned 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 period of floods. 

 The delta of Catskill creek has been found at Leeds, some 

 two miles west of the Hudson River, f The delta of Rondout 

 creek which flows into the Hudson at Port Ewen will no doubt be 

 found by following the creek back to the ancient shore line of the 

 Hudson estuary. Isolated ice-scratched bowlders are not uncom- 

 monly found in the clay. 



There is often a sharp line of division between the yellow 

 weathered portion and the blue or unweathered part of the clay. 

 The line of separation between the clay and overlying sand is also 

 quite distinct in most cases. Of the blue and the yellow clay the 

 former is the more plastic, but both effervesce readily with acid due 

 to the presence of three to six per cent of carbonate of lime, and 



*H. Rles, Rep't of N. Y. State Geologist, 1890. 

 +W. M. Oavis, Proc Bos. Soc. Nat. His. Nov. '93. 



