of Boston and itj Vichiitij, sif) 



and if conjecture may be allowed, it is jn'obable, that the ravi 

 were once outlets from these basons.* 



lues 



A small all 



the banks of Charles river. 



by 



Dedham and Needhara, bounded by Petrosilex oa the west, 



Sienite on the east, and north by Greywacke ; this probably 

 reposes on Sienite and Petrosilex, vvliich are on each side of it. 



Another alluvial deposit, of considerable extent, is found 

 stretching southeast from the Grey wacke in Dorchester, through pari 

 of quincy and Weymouth to Hin-ham. Its northeast boundary 

 is the waters of Boston harbour, and its southwest is Sienite. 

 Argillite appears in it at Quincy. 



An alluvion begins in Lynn, and runs northerly through 



Danvers, between Sienite and Greenstone; beyond the compass of 

 these observations. 



* Mr. Eaton, in his Index to the Geology of the Northern States, pubUbhcd 

 in 1818, says, that near Boston, he found fragments of Argillite, « which, with 

 other observations, induce a belief, that it may exist under the deep alluvial de- 

 posits," p. 29. We are happy to find an opinion, which we have long entertain- 

 ed, confirmed by others, with w^hom we have no acquaintance. « The whole of 

 this deposit, undoubtedly reposes an Argillite, which makes its appearance in 

 the bed of Charles river, in some places. It is found on the northern and south* 

 ern sides of this deposit, and as we know, that Argillite sometimes passes info 

 Greywacke slate, may we not conclude, that it passes under this alluvion, 

 through the bed of the river, to the Greywacke formation, and thus forms the 

 connecting link between the rocks on the north and south sides of the Charles ?" 

 Extract from ad essertation on the Mineralogy and Geology of Cambridge, by 

 S. L. Dana, read before the Linnaean Society of New England, March 29,1817. 

 The above conjecture is confined to that portion of the deposit, in the immediate 

 vicinity of Cambridge. 



y 



