700 proceedings of the academy of [oct., 



October 20. 

 The President, Samuel G. Dixox, ^I.D., in the Chair. 

 Twenty-three jDersons present. 



Inclusions in Quartz. — ^Ir. Hugo Bilgram remarked that on ex- 

 amining a section of the " Bkie Quartz " of Bucks county, Pennsylvania, 

 he had observed some very interesting inchisions. This quartz con- 

 tains small crystals of a l)luish tint, exceedingly small needle-shaped 

 crystals, some apparently opaque, and larger and smaller amorphous 

 black masses distributed in irregular groups, mostly in sheets through- 

 out the rock, probably consisting of graphite. There are also 

 numerous small cavities filled with liquid, probably water, containing 

 small bubbles. A few of these latter cavities were found to contain 

 small, loose particles which, in connection with the enclosed bubbles, 

 exhibit the phenomenon known as the Brownian movements. Some 

 are prismatic crystals or fragments, others opaque ]5articles of irregular 

 shape. These inclusions clearly demonstrate that the Brownian move- 

 ments continue indefinitely, the gneiss beds from which the blue quartz 

 originates belonging to the oldest geologic formations. 



Some of the cavities contain a number of such crystals. Owing to 

 the constant movement it was difficult to count them with certainty, 

 but he had counted no less than five or six particles in several cavities. 



These inclusions of suspended particles seem to be very rare, as he 

 had examined hundreds of splinters and had succeeded in finding only 

 a few exhibiting these phenomena. They seemed to be grouped. If 

 one cavity containing a loose crystal is found in a section, it is likely 

 that more can be discoverd by a close examination. The first section 

 in which he discovered them contains at least twenty such cavities. 

 The dimensions of the particles are exceedingly small. One of the 

 largest prismatic crystals found is about 6 micro-millimeters long and 

 about ^ micro-millimeter thick. Others are too small for even approxi- 

 mate measurement. 



Mr. Frank J. Keeley stated that he had succeeded in showing that 

 these crystals have double-refractive qualities. By placing the section 

 between two Nichol's prisms, so as to obtain a dark field, a careful 

 observation will reveal that these crystals occasionally light up as their 

 optic axis happens to become practically paralleled with the line of 

 sight. They look very much like fireflies. 



Messrs. Theodore Brooks, Allen J. Smith, Frederick L. Lewton, 

 Thomas Barbour and Edward G. Yanatta were elected members. 



The following were accepted for publication : 



