



of Boston and its Vicinity. 313 



vast masses!^ with perfectly smootli faces. Greyv/acke forms 

 hills which are rouuded and of very gentle ascent. 



VIIL ALLUVIAL DEPOSIT. 



I. This consists of sand, pebhles^ clay, and peat, and form&i 

 three varieties of soil, the sandy, marshy, and cLayey. The sand 

 is generally fine siliceous, frequently unmixed, hut often united 

 with pebbles of Granite^ Quartz, Feldspar, Argillite, Sienite and 

 Greenstone. The sand varies from very fine grained, yellowish 

 white^ to coarse, which is frequently tinged, for the extent of 

 several feet in length, and three or four inclies in thickness, with 

 Oxide of Iron; partial deposits are frequently insulated between 



primitive hills. 



II. The Peat occurs in immense beds at Cambridge, Lexins- 



fon, Newton anil Danvers. Trunks of trees, generally of some 

 of the species of pine, are frequ -ntly found in a horizontal position 

 in Peat, several feet below the surface, and in the marshes of 



Charles river. 



HI. Clay is abundant in this vicinity, particularly at Charles- 

 town, Cambridge and Danvers, and like sand, it sometime*? forms 

 sentle eminences : it is subordiaate to the Peat and Sand and 

 forms the floor on which thes? repose. This floor of Clay is very 

 much indurated, and in many places is almost as hard as Argil- 

 lite, to which it sometimes approaches. The edges of the tools of 



J, 



the well-digger are with difficulty kept sharp, when breaking 

 through this stratum ; and sometimes, the drill and the spade 

 are abandoned, and the augers used to bore through it. When 

 this is accomplished, the well is soon filled, the water enters with 

 great rapidity, and sometimes the tools are lost, and the lives of 



S8 



