1887. | MICROSCOPICAL JOURNAL. 233 
received as a gift from Mrs. W. Ashburner through Mr. Norris. They had been part 
of the collection of the late Professor. W. Ashburner, and will be cherished by the 
society which held him in such high esteem. There was also a donation by Mr. Nor- 
ris of a number of mounted slides and prepared diatomaceous material, and upon 
motion of Dr, Selfridge the thanks of the society were extended to Mrs. Ashburner 
and Mr. Norris for their generous gifts. 
Mr. Norris exhibited a slide mounted by Bourgoyne, of Paris, which contained 215 - 
distinct varieties of diatoms from the famous Santa Monica earth, all arranged in beau- 
tiful form. This slide was presented by Bourgoyne to Professor Ashburner. It is a 
most entrancing object to one affected by the datomania. 
After an hour’s discussion of current microscopical news and the relation of indi- 
vidual experiences the society adjourned. 
EDWARD J. WIcKSON, fec. Secr. 
——_Oo——_ 
The regular meeting ofthe San Francisco Microscopical Society, November gth, was! 
well attended; President Ferrer in the chair, and C. P. Bates, secretary pro fem. 
Doctor Douglas Montgomery and Doctor Kahn, of San Francisco, were elected regular 
members. 
A sample of Mono lake water was handed in by Dr. Mouser and was referred to 
Mr. Payzant for determination of crustaceans living in it. 
The paper of the evening was by Mr. Henry G. Hanks, of San Francisco, concerning 
California rock salt, as follows :— 
Some months ago I received some fine specimens of rock salt from Mr. J. S. Cook, 
of San Bernardino county, which I found very interesting, and at the same time I was 
impressed with the importance of such salt to our State and to the Pacific coast. But 
press of other business caused me to lay the matter aside for future consideration. 
Lately my attention has again been called to this very interesting subject, and I have 
discovered certain peculiarities in the mineral that I trust will be as interesting to the 
members of this society as they have proved to me. 
Like the very best quality of rock salt, this mineral occurs in blocks of the utmost 
transparency. It is quite easy to read printing through acube several inches in thick- 
ness. Some pieces are as clear, colorless and free from mechanical impurities as 
ice from distilled water, frozen in a vessel of porcelain. Others contain some foreign 
matter which does not enter into the composition of the salt. When dissolved and 
filtered the solution is perfectly colorless, and on applying the usual chemical tests, 
without observing sufficient care to detect minute traces, the salt is found to be almost 
absolutely pure. The fact that in a somewhat moist atmosphere it does not deliquesce 
is an additional proof of its chemical purity. 
Some pieces, transparent and colorless, melt at a red heat on platinum foil without 
decrepitation to a transparent and also colorless fluid, which retains its transparency 
when cooled. — 
Other specimens show faintly opalescent lines meeting-each other at right angles. 
If such a specimen is held at a certain angle in the sunlight, a multitude of reflecting 
surfaces like imbedded spangles may be seen which glimmer something like aven- 
turine, or glow like a sunstone. It may also be seen that while the faint lines meet at 
right angles, a divigling line forms a mitre like the corner of a door panel. Sucha 
specimen, when heated to redness, explodes with great violence, so much so that the 
experiment is one of considerable danger if the eyes are not protected from the minute 
flying cubes into which the larger one is broken by the explosion. 
On obtaining these very interesting results, I naturally appealed to the microscope, 
our favorite instrument, for the cause of the violent decrepitation, in one case, and quiet 
fusion in the other. Nor did I seek in vain, as I hope to be able to show you this 
evening. I found the phantom lines and reflecting spangles to be minute cavities in 
the anhydrous salt, all of the same general form but varying in size from those so minute 
as to be scarcely visible under a two-thirds objective, to others that can be examined 
in detail. The cavities are box-shaped, mostly square but sometimes slightly oblong. 
They are generally from four to six times as broad as they are deep. All the angles 
are rounded, and all the lines marking the sides of the cavities curved just as we saw 
others some months ago while examining the beautiful diamond from Amador. Both 
these minerals crystallize in the same system. 
All the imbedded cavities are empty. You may search them over and not see a 
particle of enclosed matter. But on the surface, where the walls are broken down, 
