26 SAN DIEGO TO NAPA VALLEY. 
of conglomerate rock ; but owing to the wet and boggy 
condition of the valley, we were unable to approach 
within thirty feet of them. Columns of steam. were 
rising from them on:all sides. These springs had been 
visited by Professor Shepard the year before, and some 
account of them given ‘by him to the public.* The 
temperature is said to be constantly changing.  Pro- 
fessor 8. heard that there was a place near the foot of 
Mount Helena, where the hot waters formerly flowed, 
but which had now ceased. This report induced: him 
to visit the spot. ‘‘ Externally,” he says, ‘‘ there was 
no uncommon appearance to indicate the locality. 
Neither a surplus or a scarcity of vegetation, and no 
appearance of scoria, tufa or travertine, as might have 
been expected.” In one place, however, he found it 
slightly warm on the surface; and on excavating to 
the depth of two feet, it became so hot that he could 
not bear his hand in the mud and clay. He inserted’ 
the bulb of his thermometer, and the mercury at once 
rose to one hundred and twenty degrees. The tem- 
perature of the springs we visited, varied from 105 to | 
169 degrees. 
* See Silliman’s Journal, Nov. 1851, p. 154. 
