98 
the border and down thus far into New York State, is of 
great geological importance. This is the more so, as the 
members of the Canadian Geological Survey, have only 
lately traced these rocks down into New England, as far, at 
least, as Salem, Massachusetts. 
The other specimen referred to me for examination by. 
means of the microscope, and chemically if found necessary, 
is the lump of nearly white material, exhibited by Mr. J. W. 
Ward, and thought by him to be finely-pulverized mica, and 
said to come from a bed of clay in the state of Delaware. At 
the time of its exhibition, I expressed my strong conviction 
that it consisted of the siliceous skeletons of Diatomaces, and 
my suspicions have been confirmed. In fact, strange to say, 
it proves to be a mass from the now well-known deposit, 
existing at Six mile Cafion, near Virginia City, in the state of 
Nevada, and some of which under the name of “ Electro 
Silicon,” was exhibited by another member at the same time. 
At this locality 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 christened, ‘Electro Silicon.” 
It is an example of the kind of deposit I have had already to 
allude to before this Society, 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. 
