1896.] Petrography. 209 



A Basic Rock derived from Granite.— Associated with the 

 ores in the hematite mines of Jefferson and St. Lawrence Counties, N. 

 Y., is a dark eruptive rock that was called serpentine by Emmons. 

 Smyth 4 (C. H.) has examined it microscopically and has discovered 

 that it consists of a chlorite-like mineral, fragments of quartz and feld- 

 spar. By searching carefully he discovered less altered phases of the 

 rock that were identified as granite. The peculiar alteration of an 

 acid granite to a basic chlorite rock is ascribed to chemical agencies. 

 According to the author's notion the pyrite in a neighboring highly 

 pyritiferous gneiss was decomposed, yielding iron sulphates and sul- 

 phuric acid. These solutions passed into limestone yielding the ores 

 and then into the granite changing it into chlorite. The altered rock 

 is found only with the ores. The original was probably not always 

 granite. An analysis of the altered rock gave : 



Cancrinite-Syenite from Finland.— In the southeastern por- 

 tion of the Parish Kuolajaroe in Finland, Ramsay and Nyholm 5 

 secured specimens of a nepheline-syenite containing a large quantity of 

 what the authors regard as original cancrinite. The rock is found as- 

 sociated with gneissoid granite at Pyhakurn. The rock is trachytic 

 in structure and is composed of orthoclase, aegerine, cancrinite and 

 nepheline as essential constituents and apatite, sphene and pyrite as 

 accessories. The cancrinite was the last mineral to crystallize. It 

 occupies the spaces between the other components, and yet it often pos- 

 sesses well defined hexagonal forms. It occurs also as little prisma 

 included within the orthoclase. Because of this association and because 

 the nepheline in the rock is perfectly fresh the cancrinite is regarded as 

 original. This mineral comprises 29.04% of the entire rock. 



The same authors in the same paper describe a porphyritic melilite 

 rock found as a loose block a few kilometers W. N.-W. of Lake 

 Wuorijarvi. It contains large porphyritic crystals of melilite, pyrox- 

 ene and biotite in a groundmass composed of labradorite, zeolites and 

 calcite. The pyroxenes are made up of a colorless augite nucleus sur- 

 rounded by zones of light green aegerine-augite and deep green aeger- 

 ine. No olivine was detected in any of the thin sections. 



* Jour. Geology, Vol. 2, p. 667. 



'Bull. Com. Geol. d. 1. Finn., No. 1. 



15 



