1889,] NEW YORK ACADEMY OF SCIENCES. 45- 



reached at the depth of 938 feet. This bed is 2 feet in thick- 

 ness, and is separated from the second bed, 12 feet in thickness, 

 by 4 feet of shale. The third salt-bed was 6 feet thick and 28 

 feet below the second; and the fourth bed, 9 feet below the 

 third, was 58 feet in thickness. 



Since the last report of Dr. Engelhardt, the production of this 

 mine has greatly increased, but I have not received any detailed 

 report of its business. 



The paper was illustrated with maps, diagrams, and specimens. 



Mr. a. W. Trotter made remarks upon the paper, and gave 

 some further statistics of the Retsof (Piffard) mine. 



The second paper announced was entitled 



A NOTE ON THE COLORED CLAYS RECENTLY EXPOSED IN RAIL- 

 ROAD CUTTINGS NEAR MORRISANIA, N. Y. 



BY F. J. H. MERRILL AND D. S. MARTIN. 



Mr. Merrill described the mode of occurrence of these col- 

 ored clays, which have attracted some attention of late. The 

 region is the old valley of the Bronx, which, like all the valleys 

 of this vicinity, had been much larger and deeper formerly. It 

 "was then partly filled with glacial drift, and was thereby dammed 

 up near Williamsbridge. At the close of the ice-period, and 

 during the following Champlain depression, it was occupied by 

 still water, backed up into it by the relative increase of height 

 in the sea-level, which amounted to some 80 feet. In this still- 

 water fjord was deposited a large amount of stratified sand and 

 gravel of various degrees of fineness, — some of it showing delta- 

 structure, — which was carried into it by drainage-water from 

 the north. 



The valley owes its existence, in part at least, to the fact that 

 erosion has oi)erated much more powerfully on the crystalline 

 limestone than on the adjacent gneissic rocks which form the 

 bordering ridges. [This feature is marked in the Westchester 

 region, — the valleys following the limestone belts wherever ex- 

 posed. — Ed.] 



In some places, undissolved masses of the limestone project 

 into the stratified sand and gravel ; and it is in connection with 

 these that the "colored clays" occur. The layers are of very 



