36 A GEOLOGICAL HISTORY. 



parts, as at 40th Street, near the Distibuting 

 Reservoir, all the pebbles, sand, gravel, clay, and 

 boulders, are intimately mixed, and it has the same 

 appearance at the top, as at 15 or 20 feet, below 

 the surface. 



At Corker's hook, most of the large boulders 

 lay the lowest, but yet there were some at top : in 

 many other places, the boulders were near the top, 

 gravel next, then the sharp-grained sand, usecTfor 

 making mortar ; but it must be observed, that 

 almost always, if there was any sand, it was found 

 in the lowest part of the strata : in some of the 

 hills, there would be from five to ten different kinds 

 of strata, composed of nearly the same materials ; 

 on the top, yellow, Silicious clay of one or two and 

 sometimes three feet in thickness, (which appears to 

 be an Alluvium*) then much gravel, small quartz 



* Alluvium, (a member of the Diluvium.) There was on this Island, 

 in many of the valleys or hollows, a fine yellowish-brown, Silicious clay 

 of some tenacity, which was used for making moulds and forms by the 

 founders of Iron, Brass, &c, and by masons for making a coarse cheap 

 mortar ; the localities in and about the city, are all dug out and built 

 upon — in Broadway opposite Park Place, in laying the Iron pipes for the 

 Croton water, one of these clay beds was come to, which had been partly 

 dug out, and filled in with rubbish, and which I saw but a few days ago. 

 On the Island beyond the city, in the valleys, these beds are still to be 

 found. If there is any formation, that can be called Alluvial, in my 

 opinion it is formed thus— an earthy matter, is carried up in the sap of 

 trees, or other plants, and is kept in an organized form, until the tree 

 has lived its time, when the tree dies and decays, all the matter of its 



