DIVERSITY OF THE GLACIAL PERIOD 769 



West Hills they have a thickness of over 35 feet, and reach an 

 altitude of over 325 feet above sea level. These beds are sharply 

 different from the underlying Cretaceous, and are lithologically 

 identical with the Pensauken of New Jersey. Mr. G. N. Knapp, 

 who has spent much time on the Pensauken of that state, has 

 examined the West Hills beds and believes them Pensauken, 

 notwithstanding their rather considerable altitude.^ Mr. Fuller 

 reports an additional locality on Lloyd's Neck which may belong 

 to these beds. Here the percentage of erratic material is con- 

 siderably greater, but the state of decay is much the same. 



Post-Pensauken erosion interval. — The amount of erosion which 

 belongs to the high-level interval which followed the deposition 

 of this gravel is dif^cult to determine, but the fact that all the 

 wells that have penetrated the Jameco gravels in the Jamaica- 

 Jamaica Bay valley pass into the Cretaceous without any inter- 

 vening yellow gravel bed suggests that a portion of the erosion 

 of this valley belongs to this interval. 



Jameco gravels. — The borings of the Brooklyn water works and 

 of private parties in the old Jamaica-Jamaica Bay valley have 

 revealed beds of multicolored gravels beneath beds of blue clay. 

 These gravel beds contain only 10 to 20 per cent, of quartz, the 

 remainder being dark-colored shale, red sandstone, trap, granite, 

 and gneiss. The material in these beds varies in size from fine sand 

 to small cobbles. The samples preserved by the Brooklyn water 

 works contain much more erratic material than is generally found 

 in the recent moraine. In the first sample tube* examined it was 

 believed that some careless clerk had accidentally inverted it, 

 the upper part of the tube showing yellow gravel, with only a 

 few erratic pebbles, and the lower part, below a thick bed of dark 

 lignitic clay, dark multicolored, highly erratic sands and grav- 

 els. The section seemed more correct when reversed, but, as 

 sample after sample was examined, this idea proved incorrect. 

 Records and samples collected the past summer from many wells 



' Though I have not seen the beds at this locality, I am disposed to doubt their 

 correlation with the Pensauken of New Jersey, unless, indeed, they are the glacial 

 equivalent of the aqueo-glacial Pensauken of New Jersey. — R. D. S. 



* Samples of the Brooklyn water works are preserved in glass tubes, a miniature 

 reproduction of the strata being attempted. 



