442 THE POPULAR SCIENCE MONTHLY. 



With the specimens before us, we think these surface-beds, to a 

 depth of about 180 feet, are post-glacial, and are formed from glacial 

 drift.. Below this depth the beds are of dark clay and clayey silt- 

 like sand, alternating with deposits of sand similar to that of the 

 beaches upon the coast. Lignite occurs throughout, and a layer of it 

 at 353 feet was penetrated with difficulty by theimplements employed 

 in boring the well. 



The lignite found throws little light on the age of the beds. It is 

 brought to the surface in small pieces, and that from the surface of 

 the clay bed at 353 feet was formed from small stems of exogenous 

 structure. The same is true of that found on the bed at 70 feet. This 

 deposit of clay, 56 feet in thickness, seems closely analogous to many 

 clays now upon, and at various depths beneath, the siirface of the island. 

 It is evidently a local deposit, such as might occur in a depression of 

 the surface. Two tube-wells have been driven at no great distance 

 from Barnum's Island, one 97, the other 194 feet, in which no similar 

 layer of clay was detected. No green sand or marl deposits have 

 been found. It seems probable that the beds below a depth of 180 

 feet were formed in tranquil waters of no great depth, possibly in an 

 estuary sheltered by a beach of sand from the waves, into which 

 streams discharged the waste of what was evidently a forested region. 

 That they are preglacial, is, we think, quite certain. The period 

 of transition between the Tertiary and the Drift, when the distant 

 but advancing ice-sheet sent on its swollen streams, best answers the 

 conditions. The existence of beds of stratified gravel and sand at 260 

 feet above the level of the ocean, and of similar beds at 180 feet below 

 it, which we refer to the period of the Champlain subsidence, proves 

 that a depression took place of at least 440 feet, and further that the 

 coast was at least 180 feet higher than now when the depression be- 

 gan. That the elevation was much greater than that will be obvious 

 as we proceed. 



The glacial drift of Long Island, of which the Champlain deposits 

 were formed, is without fossils, excepting such as occur in bowlders 

 from older beds. But underneath it is a deep deposit of sands, grav- 

 els, and clayey sands, in which fossils have been found. Shells of the 

 clam and oyster were taken from sands beneath the bowlder-drift at 

 Lakeville, at a depth of 140 feet, by Henry Onderdonk, Jr., Esq., and 

 a mass of shells, chiefly oyster, were found in sinking the well of the 

 Nassau Gas-Light Company in Brooklyn, 127 feet below the surface, 

 beneath a layer of unmodified drift, 70 feet thick. In this drift were 

 many bowlders. A section of this well is shown in Fig. 3. 



In digging wells these sandy and gravelly layers are generally 

 found beneath the bowlder-drift; and the shells, wood, and lignite, 

 evidently represent a period of milder climate than prevailed during 

 the Ice period. Possibly they were deposited on the coast by the 

 floods and swollen streams of the approaching glacier, and the coarse- 



