1897 THE MICROSCOPE. 163 
Obsidian. 
By W.S. BEEKMAN, 
WEST MEDFORD, MASS. 
One of the amusing anecdotes given by the famous 
Stoddard, in his lectures, is somewhat like this: An old 
scout whose aim with the rifle was always of unerring 
certainty, being within the grand Yellowstone, came 
suddeuly one day face to face with a monstrous bear. 
He fired and was surprised to find that the animal re- 
mained quietly about its own affairs, With great preci- 
cision he tried again, but he found his aim was not pro- 
ducing results. Advancing towards his victim he found 
himself against a great glassy wall. It was through a 
mountain of obsidian he had been looking and his bear 
was still on the other side. This must have been when 
Obsidian was more crystalline clear than it now is. 
To the student, this volcanic glass has often been the 
means of similar wasted efforts. [tis simply afused glass 
without detail. In some specimens, however, may be found 
the peculiar minute detail that brings it within the class 
of objects for slide study. When the development of 
crystallites has become so advanced that a partial devit- 
rification ensues, as in the variety called Pitchstones, 
slides for polarized-light are possible. The writing of 
the present article is due to the fact that a quantity has 
been found which has formed the aggregation of its crys- 
tallites in fairly minute concretionary spherules, The 
flow-structure of this highly acidic lava is thus made on 
a small enough scale to be used as an opaque mount, The 
concretionary spherules, however, might bring out some 
very interesting features, if prepared. The writer has a 
lot of these interesting specimens, and would be pleased 
to send some to any one who sends a stamped addressed 
envelope. 
