WILLIAM B. DWIGHT. 91 



layers ; the outer and earlier ones being conformed to 

 the outlines of the conical mass, though they became 

 nearly level at the bottom ; the inner layers, however, 

 became less and less steep as the pit filled up, so that the 

 highest and most central ones were very shallow basins, 

 approximating to horizontality. Marked exceptions to 

 this regularity of deposit occurred at the lower part of 

 the mass, near the level of the floor above mentioned. 

 Here there were two or three mounds of clay, which, to- 

 gether, covered the greater part of the horizontal area 

 of the clay-bed at that level, and in which the various 

 layers formed inverted cups — precisely the reverse of the 

 position of the layers in the general mass. These 

 mounds were from ten to sixteen feet high (fig. 1). 



This inverted cone (or conical basin, as we may call it, 

 if we regard rather the envelope of sand enclosing the 

 clay) has an elliptical cross-section of about eighty by 

 fifty feet at the lowest floor-level mentioned, and about 

 one hundred and fifty feet for its longest diameter (esti- 

 mated) at the top. The shorter diameter is parallel to 

 the course of the river at this point. 



The clay is quite calcareous, and its layers are occa- 

 sionally separated by thin layers of very fine sand. A 

 few large boulders are found scattered through the clay 

 deposits, but there are no beds of gravel nor of coarse 

 pebbles within them. As the successive layers were un- 

 covered in the working of the pit, the fresh surfaces, 

 after a short exposure to the air and rain, soon became 

 superficially hardened in curious lamellar and nodulous 

 shapes ; probably through the' cementing agency of the 

 calcareous ingredients combining with the sand present. 

 This mass of clay everywhere rested upon or abutted 

 against fine sand, itself evidently stratified, or, more 

 commonly, the edges of the various clay-layers shaded 

 off into alternate layers of clay and fine calcareous sand 

 (s., figs. 1, 2, and 3). 



75 



