RECORDS 491 



Prof. C. L. Bristol, of New York University, as Chairman, and 

 Prof F. E. Lloyd, of Teachers College, as Secretaiy for the 

 ensuing year. 



Francis E. Lloyd, 



Secretary. 



SECTION OF GEOLOGY AND MINERALOGY. 



May 2 1, 1900. 



Section met at 8:15 P. M., Dr. Alexis A. Julien presiding. 



The minutes of the last meeting of Section were read and 

 approved. 



The following program was offered : 



George I. Finlay, A New Occurrence of Nephaline- 

 Syenite and Associated Dikes in the State of Tamaulipas, 

 Mexico, with a Review of the Distribution of these Rocks 

 IN North America. 



Benjamin F. Hill, A Contribution to the Geology of a 

 Part of Sonora, Mexico. 



Summary of Papers. 

 The rocks described by Mr. Finlay were sent by Mr. E. D. 

 Self to Professor Kemp of Columbia University. The nephaline- 

 syenite is a very light colored rock, containing, besides abundant 

 nephaline and anorthoclase, small patches of the dark colored 

 silicates. Under the microscope these are seen to be aegerine- 

 augite intergrown with hornblende, and accompanied by magne- 

 tite and apatite. Titanite is abundant, with the faces (1-2-3) 

 well developed and some zircon occurs. The tinguaite asso- 

 ciated with this syenite is a holocrystalline porphyritic dike rock 

 with large phenocrysts of orthoclase, twinned on the Carlsbad 

 law, tabular in habit, parallel to the clinopinicoid. The ground 

 mass, which gives the rock an even, dark green color, consists 

 of a felt of tiny blades of aegerine and orthoclase. The aegerines 

 are at times grouped together in bundles around small patches 

 of biotite. 



