Geology and Natural History. 481 
these are solvents for quartz and sulphides of the heavy metals. 
s of the mi ; d to 
“should be confined to the neighborhood of this contact,” and 
“should this rock narrow to a mere dike between diorite walls, 
”? is 
temperature and pressure, they w ave t decomposing 
and carrying powers; nothing as to whether the wall of the great 
re may no ave contained metalliferous veins 
rate of about 3° F, for each additional hundred feet. “On the 
3,000-foot level” —to which depth the country is honey-combed 
with passages—“ floods of water have entered the mines at 170° 
F.,” hot enough to cook food. The equation deduced from the facts 
gives for a temperature of 212° F. a depth of 5,200 feet; and “a 
boiling heat is likely to be struck at any time after passing the 
4,000-foot level,” and in all probability short of 5,000 feet. 
The facts show that the source of the heat “can hardly be less 
than two miles from the surface, and is probably four, in short at 
apne 
4 volcanic distance. In the Sutro tunnel “the rise of temperature 
as the lode was approached is best expressed by a geometric 
ratio,” showing that the heat is derived from the lode, the moist- 
re or aqueous vapor present enabling the rocks to conduct heat. 
Am. Jour, a Series, VoL. XXVI, No. 156.—Dec., 1883. 
