44o i THE POPULAR SCIENCE MONTHLY. 



which the glaciers had left were altered in their contour, and redis- 

 tributed by waters which encroached upon and finally covered them. 

 The material thus redistributed would be left in layers, chiefly of 

 gravels, sands, and clayey sands, if upon the ocean-margin, as is the 

 case in Long Island. 



In sinking wells into the beds formed during this period of sub- 

 sidence, wood and shells have been found in a great number of in- 

 stances. The wood sometimes occurs in logs of large size; oak and 

 pine have been identified. We have a record of sixteen instances 

 where wood has recently been found, and many others are mentioned 

 by Thompson in his history, and by Mather in his excellent report on 

 the geology of the island. These facts seem to imply that forests 

 were upon the adjacent lands, which was not the case during the 

 presence of glaciers upon the coast. 



The shells found are at various depths in one case at Gravesend 

 100 feet below the surface and occur in all parts of the island where 

 the stratified drift abounds. They have been found at Flatbush, 

 Prospect Park, Bath, East New York, Farmingdale, Amagansett, 

 and elsewhere. 



The beds in which they occur are not of the low plains only, but 

 many feet above tide. At Manhassett, as we are informed by John 

 M. Clark, Esq., of that place, a well was dug, and at several feet below 

 the surface-rubbish a layer of what appeared to be " creek-mud " was 

 found, in which were a great number of shells of the oyster, clam, and 

 scallop, many of them unbroken. The layer was about five feet 

 thick, and throughout contained not only shells, but leaves, pine- 

 cones, also wood of pine and other species. This interesting deposit 

 is about 200 feet above tide ; but the contour of the present surface 

 indicates plainly enough that an arm of a bay (Little Neck Bay) 

 contiguous extended over this area when the land was sufficiently 

 submerged to admit of it. 



It is obvious that only the portion of Long Island which is more 

 than 200 feet above tide was at that time dry land. 



But the subsidence was greater than is indicated by this elevated 

 deposit. The peculiar beds of stratified sands and gravels on the low 

 plains already referred to, and which prove the former presence of the 

 sea, are found at elevations of from 200 to 260 feet along the margins 

 of the hills, and against or upon the unmodified bowlder-drift (Fig. 2). 

 Beach-sands occur at 230 feet elevation, having the well-known struct- 

 ure of such beds. We have, too, the further fact, already noticed, 

 that the tops of some of the highest hills of our island are composed 

 of stratified gravel and sand. 



AVithout insisting further on, this fact, however, we think a move- 

 ment of subsidence is shown thus far of at least 260 feet ; but facts of 

 a most interesting and important character now being brought to 

 light show that this is but part of the great movement of depression 



