of the Yellowstone and Firehole Rivers. 111 
mountain than those along the immediate margin of the river. 
Near the head of the East Fork of the Yellowstone there are 
two or three localities where these calcareous deposits cover 
limited areas. At one locality near the margin of the stream, 
there is a very instructive mound, about fifty feet high, with a 
broad base of 150 feet, rising more gradually to the summit, 
which is broad, mammiform. The deposit was originally made 
in thin layers overlapping each other like a thatched roof. 
This was undoubtedly at one time a spouting spring. It com- 
menced with a very moderate force, nearly overflowing its basin, 
and building up about 10 feet in thickness of thin, nearly hori- 
zontal layers; then it commenced gradually rising until it 
reached a height of about 50 feet, when it closed itself up at 
the summit and died out. There is not a sign of water in it at 
the present time, and none of the springs in the vicinity are 
above the temperature of ordinary spring water. 
We must omit an account of the basaltic columns ex 
pai and white; much of the deposit 1s as w ite as snow. 
rendering it oppressive with sulphurous odor. This group ex- 
tends oo. sia Sadia to the eastward for several miles. 
