296 King’s Systematic Geology of the 40th Parallel. 
The 17382 level affords us the best evidence that the inces- 
sant drain of heat cannot be maintained by supply from a store 
accumulated in the rock. This drift was probably completed 
by January 1, 1876, or perhaps some months earlier. It has been 
constantly in use as an air way, but after this long exposure no 
diminution in its heating power has been noticed. It has lost 
the intense heat it had when first opened, but remains at an 
average temperature of about 90° F. 
Art. XXXVI.— United States Geological Survey of the Fortieth 
Parallel. Vol. I. Systematic Geology ; by CLARENCE KING. 
Reviewed by RAPHAEL PUMPELLY. 
THe February number of this Journal contained, in_the 
form of citations, a summary of the results of the Fortieth Par- 
allel Survey in the department of Stratigraphical Geology. 
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