1214 Outlines of the Mineralogy and GeoU2;tf 



tbe workmen are eudangered. It is necessary to descend from 

 70 to UO feet to penetrate through this Clay ; under this, appears 

 to he, in some places, fine sand. These facts we learn from the 

 wells, whicli Lave been dug in several places. The pebhles and 

 sand, or sand and clay, are not unfrequently disposed aternately 

 in strata, which are from five inches to several feet in thickness. 

 Often in these strata are found smooth rounded stones like those 

 wliich occur on sea beaches ; tliese stones are found at a great 

 depth, and with the fine sand which they accompany, are often an 

 indication to tlie well-digger that water is not far distant. 



IV. The only organick remains, which have been observed in 

 the alluvial deposit, are the trees above mentioned, and marine 

 shells, which occur in Cambridge. A stratum of clam-shells 

 frnya arenariaj was exposed a few years since by a violent rain ; 

 it was on the side of a hill, distant about ^ mile from the river. 

 Its extent was several feet and its thickness three or four inches. 



■V 



Some of the shells were quite perfect, but generally much com. 

 minuted. At Lechmere Point also deposits of shells have been 

 found from five to ten feet below the surface ; these strata are several 

 iaclies in thickness and several feet in extent. A stratum of clam- 

 shells and muscle-shells {'mya etmytiliisj is sometimes separated 

 by a stratum of black loam, six or eight inches thick, from a stra- 

 tum consisting chiefly of oyster- shells fostrea edulisj ; shells of the 

 same species are now found in the river ; but others occur, which 

 are not found nearer than Chelsea and the waters in the harbour 

 of Boston. Fragments of the mya arenaria have been found forty 

 feet below the surface at Jamaica Plains, and Loam mi Baldwin 

 Esq. shewed us the fragment of a clam-shell found at the depth of 

 107 feet, in digging the well at Fort Strong. 



