PETROGRAPHICAL PROVINCE OF ESSEX COUNTY 109 



100.33 100.97 99.95 



I. Quartz-Syenite-Porphyry. Squam Light. H. S. Washington anal. 



II. Nordmarkite. Wolf Hill, Gloucester. H. S. Washington anal. Jour 

 Geol., VI. p. 800, 1898. 



III. Lindoite. Fron, Norway. V. Schmelck anal. Brogger : Eruptivgest. des 

 Krist. geb. I, p. 139, 1894. 



The composition is rather acid, with high alkalies and rather 

 high lime, with ferrous oxide largely in excess over ferric, and 

 is closely similar to that of the nordmarkite. These dikes 

 resemble in certain ways the lindoites of Brogger, which are 

 acid bostonitic rocks. This is seen from the chemical point of 

 view by comparison of I and III, that of the Essex county rock 

 differing materially only in the slightly higher lime. Mineral- 

 ogically they also resemble each other closely, though blue 

 arfvedsonite or riebeckite is common in the lindoites, while the 

 hornblende here is a peculiar green with only a tinge of blue. 

 One specimen of lindoite in my possession from Huk in the 

 Christiania Fjord, collected under the guidance of Professor 

 Brogger, shows greenish -brown hornblende with some biotite, 

 and does not differ radically from the present dike rocks. 

 Structurally also the two resemble each other, the groundmass 

 feldspars being quite automorphic in stout tables, the quartz 

 interstitial and the hornblende irregular. 1 We do not, however, 

 find in our rocks the zircon which is so common in the Norway 



1 Cf. Brogger, op. cit., I, Fig. 15, p. 137. 



