73 
storms, often resulting in sudden inundations. Such an inun- 
dation was observed by the expedition in 1865, near Fort 
Berthold, a wall-like mass of water ten to fifteen feet high, 
rushing down a small dry watercourse, on which the expedi- 
tion was camped. In the narrow gorges of the Bad Lands of 
the Little Missouri, the effect of these floods was observed by 
the presence of tree-trunks and brush-wood, at a height of fifty 
feet above the level of the then dry water-courses. During 
both expeditions, the nights were bright with auroras, some- 
times for weeks in succession, and especially is this the case 
between Fort Berthold and Devil’s Lake, and in the neigh- 
boring sections of country. 
October 24, 1870. 
The President in the chair. ‘Twenty-four persons present. 
Dr. L. FEUCHTWANGER, exhibited a specimen of a mineral 
which has gone by the name of Onoprite. It is a Selenio- 
Sulphide of Mercury, and was first obtained by Del Rio near 
San Onopre, in Mexico. H. Rose has made an analysis of it 
showing it 6:49 per cent. of Selenium, 10°30 of Sulphur, and 
81:33 of Mercury. The specimen exhibited was not from 
the original locality in Mexico, but from the Santa Clara 
Mine, in Lake County, California, near Clear Lake. It was 
of particular interest, on account of its locality, being asso- 
ciated with the Cinnabar of California. Lately it has had 
the name of Tiemanite bestowed upon it. 
He also exhibited specimens of Stream Tin Ore from Durango, 
Mexico. This resembles so closely the Stream Tin of Cornwall, 
England, that they cannot be distinguished. Unfortunately 
labor is so precarious, and other attendant circumstances are 
so unpropitious, that the working of this ore at Durango, has 
not been prosecuted so that the English mines still continue 
to supply the major part of the Tin of commerce ; although 
the new Missouri mines promise very well, ores yielding as 
