PE TR O GRA PHICAL PR O VINCE OF ESSEX CO UN TV I 2 I 



content of water. It very closely resembles the Hedrum border 

 rock, except in water and potash. The biotite-tinguaite is more 

 acid, and closely corresponds in general features to the analysis 

 of the Coney Island solvsbergite. The characteristic distinction, 

 however, is found in the relative amounts of the iron oxides and 

 in the alkalies. In these respects the two tinguaite analyses 

 resemble each other, and these two features, taken together, 

 serve to differentiate their analyses from those of the more basic 

 solvsbergites. This whole series presents several points of inter- 

 est, as regards the relations of the various members to each 

 other, and their relative composition, but discussion of these 

 features will be deferred to a later page. In connection with 

 these rocks I may call attention to a so-called phonolite from 

 Southboro, Mass., whose analysis is given in VI. Although not 

 described an examination of sections of specimens kindly sent 

 me by Professor B. K. Emerson proves that they are typical 

 aegirite-tinguaites, one specimen showing very sharp nepheline 

 crystals. 



Henry S. Washington. 



(To be Continued) 



