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BOULDERS DUE TO ROCK DECAY. 
By Warren Upham, St. Paul. Minn. 
Last summer, visiting Butte, Montana, in my return from 
a trip to the Puget Sound region, I was greatly interested in 
the wonderful abundance of boulders which have resulted 
from the decay of the Butte granite upon large parts of its ex- 
tensive area. Derivation of many boulders in the glacial drift 
from similar preglacial surfaces strewn with loose rock masses, 
ready to be carried away by the ice-sheet, has therefore ap- 
peared to me highly probable, and indeed demonstrable, which, 
though before partially recognized, has never, as I think, been 
accorded its proper degree of importance. 
This granite intrusion, as described by Walter H. Weed 
in the Butte Special Folio, No. 38 of the U. S. Geological 
