60 The Mountaineer 
in this fashion we tried to sleep on the steep angle of the crater. 
Fortunately there were several large rocks above which we 
made our beds. We were careful not to push too much against 
these rocks for we were afraid that they might break loose. 
Bad as were these conditions the night was passed more com- 
fortably than a night is spent at Camp Muir or Camp Curtis 
in a cold wind. 
Strangers would not think that the small openings under 
the crust of snow or ice could lead into such large chambers 
within which several hundred people could find warmth and 
shelter. At times the roofs of these caves must collapse to the 
floor, just as the ice caves do where the water rushes out of the 
end of a glacier. This uncertainty makes a man feel rather 
uncomfortable when he realizes what might drop on him while 
he is within. The steam comes quite fast, at fixed intervals like 
the breathing of a large animal. The steepness of the slope, 
the danger of collapse, the puffing of the steam, the pitch dark- 
ness, and the general hell-like surroundings all taken together 
make indeed a novel situation which one will remember for a 
long time. 
Near these caves are several kinds of moss and the com- 
mon liverwort (Marchantia polymorpha). These have never 
been observed in the fruiting condition. 
These thermal caves formed between the ice and the crater 
rim or on the slope of Crater Peak must not be confused with 
the lava caves which are so common to the south of Mount 
Adams. The eause of their formation is entirely different. 
There are no lava eaves in the vicinity of this mountain. They 
are caused by the cooling of the outer surface into a crust while 
the inner portion remains liquid and flows on, leaving an empty 
shell often half a mile or more in length. They are more per- 
manent than the thermal caves which have only ice for a roof. 
These thermal caves vary as the snow varies from year to year. 
They can only be formed where the steam issues forth and the 
snow accumulates in such quantity as to form ice. 
