1878. ] Microscopy. ` 491 
Feannette (Pandora) will be ready for sea in a short time, and 
then sail for Havre, where a temporary crew will be shipped, 
when she will leave for San Francisco. Mr. Bennett hopes the 
expedition will sail for the North in June, 1879. It will go by 
the route through Behring’s Straits. Prof. Nordenskiold’s ex- 
pedition for the north-east passage sails in the Vega, in July. 
The vessel Eothen, with twenty-five men, will sail from New York 
-in July for the Arctic regions in search for the relics of Sir John 
Franklin. 
MICROSCOPY .! 
DETERMINATION OF ROCKS BY THE Microscope.—At the regular _ 
meeting of the San Francisco Microscopical Society, May 16th, 
Mr. Melville Atwood presented twenty-two rock specimens illus- 
trating a new method of preparing the same for determination, 
and read a very interesting paper on the subject. He is aware 
that looseness in petrological nomenclature is the rule and not 
the exception, and that many geologists are found writing of 
totally different rocks under the same name. But he is still more 
impressed with the ignorance of the miners in regard to the rocks 
which form the boundaries of the different mines. He does not 
value much any distinction between rocks which cannot be 
applied in the field, and he found, while making a collection of 
rock specimens prepared in different ways, that what was most 
wanted was a method to make it easy for his fellow-miners to 
understand and distinguish the enclosing and wall rocks of the 
different lodes they were working—these rocks having so much 
. to do with the productiveness of the lodes. To prepare rocks so 
that they can be easily studied with a pocket lens or a low power 
of the microscope and accurately identified by comparison with a 
collection of foreign types, they are prepared as follows: “First 
wash the specimen clean, using a brush to get rid of any clay and 
dirt; then select the side or part you wish to examine, and grind 
it down on a piece of sandstone (a shoemaker’s sharpening stone) 
until a perfectly flat surface is obtained. This will occupy but a 
few minutes unless the rock is very hard. The surface should 
then be worked down still finer with a-square emery file, using 
water, and after you have obtained a sufficient polish, wash the 
rock again and then let it dry gradually, either on a stove or, 
what is better still, a little brass table with a spirit lamp, the same 
that is used for heating slides. When perfectly dry heat it again 
to a point so that you can barely handle it; then varnish the pol- 
ished side while hot with a mixture of one part of Canada bal- 
sam to three parts of alcohol, which must be warmed before 
applying it, and laid on with a camel’s hair brush. It will soon 
dry, and if left for a day or two will harden, so that you can han- 
dle it without injury.” This simple and rough treatment is 
1 This department is edited by Dr. R. H. Warp, Troy, N. Y. 
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