■^ 



^08 



Outlines of the 



Mineralogy and Geologif 



change than Greenstone. It occasionally becomes so much disin- 

 tegrated as to form gravel and sand ; this occqrs at Danvers and 



Lynn. 



IX. Greenstone and Sienite are composed essentially of the 



ulty frequently 



Hornblende and Feldspar, and 



diffi- 



The gereral col- 



of the rocks, and the particular colour of some of their com- 

 parts have been employed to assist us in distinguishing 



Sienit 



them ; the Feldsp 



shade of red, while Greenstone, has 



green, not only in the Feldspar but in 



g' 



g 



h 



some shade of 

 lass : this rare- 



ly sccurs in Sienite ; Greenstone seldom contains any considera- 

 ble proportion of Quartz; but in the Sienite of this vicinity. 

 Quartz forms a constituent part ; this circumstance, connected with 

 the general reddish white colour of the rock, will sufficiently dis- 



£,....« the 



X. Sier 



of the most valuable rock 



IR 



part of 



with ease into large blocks and tables. Vast 



quantities are annually brought from B 



to Boston, for \\\f- nnrnncoc ^f U.,;i,i; 



and Weymouth 

 The Stone Chapel h 



Boston, the State Prison, and the Prison at Lechmere Point 



built of Sie 



At Danvers, it is wrought into mill-stones, and 



many parts of the Union are supplied with them fi 



Pl 



VI. AMYGDALOID. 



I. Amygdaloid is ranked with transition trap 



It 



rock 



posed, that the 



homogeneous basis, which does not appear to be cotemp 

 with its imbedded simple minerals ; hence it has been sup 



d that the cells have 



ubsequently filled, the form of the imbedded miner 



% 



nj|. 



.^1 



