228 Microscopical Examination of Two Minerals. 



the state of Nevada, and some of which, under the name of " Electro- 

 SiHcon " was exhibited by another member at the same time. At 

 this locaUty this remarkable material is reported to occur in the 

 form of a stratum several hundred feet in thickness. It is rather 

 hard and stony, so it is ground down to a fine powder, and then 

 comes into commerce as a polishing material, and has been rather 

 fancifully chi-istened " Electro-Silicon." It is an example of the 

 kind of deposit I have had already to allude to as Sub-Plutonic, 

 examples of which are so common all through our Pacific States. 

 At some future time I will have something to say concerning the 

 genesis of these deposits. 



We have in these two examinations, which I have been enabled 

 to make, further evidence, if it were necessary, which fortunately it 

 is not, of the value of a knowledge of the means of employing the 

 microscope to the geologist ; for, using it, facts have been thus 

 readily and in a few minutes settled, which no chemical or other 

 analysis, taking perhaps hours to perform, would indicate. — From 

 Proceedings of Lyceum of Natural History, New Yorh, U.S. 



