/ 



% 



of Boston and its Vicinitj/, 



SSi 



Amygdaloid. 



(Coloured Vefmillion rcA) 



This forms the rocks at the Lower Falls^ Newton, and agaiu 

 appears in Brighton and at Needhara ; whenever it is found, it 

 occurs at the borders of the Greywaclie formation. It is found 

 also in Hingham^ associated with Greywacke. 



Petrosilex. 



(Coloured blue.) 



A narrow strip, running south-east and north-west, from 

 Quincy to the western part of Roxbury ; its extremities disappear 

 under alluvial soil ; its northern edge is hounded by Greywacke, 

 and its southern is associated with Sienite, into which it some- 

 times passes. It again appears in Needham, where it forms a 

 high pyramidal rock, called High Rock ; at this place the Petro- 

 silex is almost porphyritick ; is of a greyish colour, having small 

 hyaline grains of Quartz disseminated in it. 



Another formation of Petrosilex begins at Medford, and runs 

 nearly east and west ; its south border meets the alluvion, and 



north passes 



Porphyry 



m 



Maid 



dLy 



fre 



quently appears among the Porphyry 



Nahant rocks are formed 



Petrosilex ; and it appears also contiguous to Grey^vack 



Nantasket beach in Hing 



Argillite, 



(('oloured black.) 



This for 



ulated hills in Watertown and Charlestow 



A part of Prospect Hill and the whole of Winter Hill are formed 

 by ArgilUte; it extends from Charlestown neck, north-westerly, 

 and it disappears under alluvial soil. Argillite again appears 

 between the Alluvion and Sienite, in Quincy, and Petrosilex and 



S94 



4» 



