PETROGRAPHICAL PROVINCE OF ESSEX COUNTY 63 



tion products, these are the only minerals present. An analysis 

 was made of the freshest specimen, which was slightly altered, 

 from near a cove on the north shore of Nahant, east of the 

 village. 



Si0 2 - - - 43-73 Na 2 - - - 2.42 



Ti0 2 - - 4-23 K,0 i.45 



AI0O3 - 20.17 H 2 0(no° — ) - - - 0.08 



Fe 2 3 - 4-32 H 2 0(iio°+) - 1.02 



FeO - - 6.93 P 2 5 - - 0.15 



MnO ... - none 



MgO 3.91 99- 4o 



CaO - - - - 10.99 



It is low in silica, rich in lime, but rather poor in magnesia, 

 high in titanium oxide and alumina, and rather high in alkalies 

 for such a rock, which is evidently a true gabbro. 



ADDENDUM 



" Hyperitic diorite." — Since the description of this rock was put in 

 type an analysis has been made, which renders necessary some correc- 

 tions and additions. The analysis is given here. 



1 11 



Si0 2 45-32 49-25 



Ti0 2 - - 1.94 i-4i 



A1 2 3 - 18.99 l6 -97 



Fe 2 3 - - - 3.78 ) 



23 \ 15.21 



FeO - 9-78 \ 



MnO - - trace 



MgO- - - - 4-68,/ about 3.00 



CaO - - - 9-19.' 7-17 



Na 2 - - 3-78 4-9 1 



KoO - - - 2.12 2.01 



P 2 5 0.76 



about 0.30 



H 2 (no") - - 0.09 



H 2 0(ignit.) - 0.31 



99.98 100.99 



I. Hornblende-gabbro, Salem Neck. H. S. Washington anal. 

 II. Olivine-gabbro-diabase, Dignses, Gran. A. Damm and L. Schmelck anal. 

 (VV. C. Brogger. Quart. Jour. Geol. Soc, Vol. L, p. 19, 1894.) 



