PETROGRAPHICAL PROVINCE OF ESSEX COUNTY I 1 9 



The Andrew's Point solvsbergite is rather acid and approaches 

 closely the katoforite-solvsbergite from the Lougenthal. It 

 resembles the Coney Island dike in its main features, especially 

 in the high alkalies and the relations of the iron oxides. The 

 two analyses of the Cone)' Island dike resemble each other very 

 satisfactorily, and show that it is rather more basic, approaching 

 the Kjose-Aklungen dike, which, however contains a little nephe- 

 line. It is evident from these analyses and the descriptions 

 given that the Coney Island rock is really a solvsbergite and not 

 a bostonite-porphyry, for which indeed, as Rosenbusch himself 

 remarks, it carries an abnormally large amount of colored min- 

 erals. 



Tinguaite. — The most basic members of the series we are 

 now discussing, the tinguaites, which are not abundant in Norway, 

 occur very sparingly in Essex county, only three dikes of this 

 rock having come to my notice. 



One of them, an analcite-tinguaite, from Pickard's Point near 

 Manchester, has been already described. 1 It is aphanitic and 

 olive-green, with only rare phenocrysts of feldspar in a ground- 

 mass of aegirite needles, alkali-feldspar, nepheline and analcite. 

 The perfect freshness of the rock, as well as theoretical consid- 

 erations, lead to the conclusion that the analcite is primary. 



The second tinguaite occurrence is that recently described by 

 Dr. A. S. Eakle 2 as a biotite-tinguaite from Gale's Point near 

 Manchester. It is composed of alkali-feldspar, nepheline, kao- 

 lin and secondary quartz, aegirite. and a little biotite and mag- 

 netite. As Dr. Eakle points out it approaches the nepheline- 

 bearing solvsbergite from Kjose-Aklungen already mentioned, 

 and might be classed with the solvsbergites. 



The third occurrence of tinguaite is a dike two hundred yards 

 east of Squam Light, discovered by Mr. Sears, to whom I am 

 indebted for a specimen, The rock is dark green and very 

 dense. This is also a biotite-tinguaite and very fresh. No 

 phenocrysts are visible. Abundant small irregular grains and 



■H. S. Washington, Am. Jour. Sci., (4), VI. p. 182, 1898. 

 2 A. S. Eakle, Am. Jour. Sci., (4), VI, p. 489, 1898. 



