Dr John Davy on Oxide of Arsenic. 47 
very doubtful, judging from the circumstance that its 
fructifying power was not apparently impaired, seed-vessels 
being abundant on it. At my last visit I saw sheep 
browsing on the grass that grew at the edge of the stream : 
and then I was struck not only by the variety of the kinds 
of plants, but also by the freshness and healthy appearance 
of those so near as to be in the way of being sprinkled with 
the spray of the little torrent. At the same time that I 
had the advantage of the company of Dr Robinson, we 
sought for larve in the sediments of a little pond, which 
had been formed as a reservoir for the purpose of working 
a mill belonging to the farm, but without success. The 
only living things we saw, and these were not in the water, 
were some small spiders, which were actively skimming its 
surface. In a portion of the sediment which I brought 
away, subjected to the microscope, I found a few remains of 
Infusoria. It may be worth mentioning, that when the 
bottom of the pond was stirred much air was disengaged. 
Dr Robinson was so good as to have a portion of it collected 
and sent tome. I found it to be almost entirely azote ; it 
was not diminished by agitation with milk of lime, and 
hardly perceptibly by phosphorus; nor was it inflammable. 
As the deposit had an ochrey hue, perhaps the separation of 
the oxygen, which most waters contain, was owing to the 
action of a protoxide of iron in process of conversion into 
the peroxide. 
To revert to the arsenical impregnation. If it be asked 
whence it was derived, we have not far to seek: the obvious 
inference is, that the very minute quantity of arsenic in the 
water is owing to the water flowing over mineral substances 
of which arsenic is a constituent part, such as arsenical 
pyrites, which I am informed was abundant in the mine,— 
(a vein that was worked for cobalt), and is of common occur- 
rence in the side of Black Comb. Dr Robinson, who had 
collected some specimens of it, favoured me with a portion 
of them ; and from water, in which they had been immersed 
a few hours, traces were detected of oxide of arsenic, and 
also of iron and copper; and in confirmation, I may state, 
that when, at my last visit, I tested on the spot the two 
streams before adverted to, which by their junction form 
