106 ERYTHEA. 



longer second ridge lies parallel to this: its northeastern extremity 

 ends in cliffs; its southwestern extremity is less abrupt, the ultimate 

 termination being a lateral spur lying in nearly the same direction. 

 The short sharp third ridge lies at nearly right angles to the second ; 

 its highest point is the highest point of tlie mountain, and on it are 

 located the piers of the signal station of the United States Coast and 

 Geodetic Survey. 



The entire summit and the abrupt sides above 2,300 or 2,400 feet 

 are covered with a slieet of volcanic ash, mostly in the form of loose 

 somewhat finely broken rock. There is nothing that can be called 

 soil above 3,000 feet, and there is no spring on or near the trail from 

 2,300 feet up to the signal station piers. Indeed, so far as my 

 knowledge extends, water can not be found anywhere above the 

 altitude just named. 



On account of its volcanic character and the scarcity of water, 

 the number of species to be found on the summit is very small. 

 Meager as the vegetation is in number of species, yet, doubtless, the 

 number of species would be even less were the mountain located in 

 the Inner, instead of the Middle, Coast Ranges. Its situation is in 

 a region of great annual rainfall, and the fogs hang about the moun- 

 tain at intervals during the rainless season for a portion of the day 

 for a period of several days to a week or more. 



The general conditions may be compared with those of Mt. Diablo, 

 which lies to the southeastward of Mt. St. Helena and distant sixty- 

 seven miles from it. The number of species on the summit of 

 Diablo, taking the list* of Prof. Greene" as a basis, is over four 

 times as great as the number enumerated below from St. Helena, 

 notwithstanding that the former region is one of less annual rainfall 

 and that summer fogs seldom reach as far inland as Mt. Diablo, and 

 in such cases the summit is commonly enveloped but for a few hours. 



The difference in the humidity of the two regions is readily to be 

 inferred by the traveler. Fertile valleys and low hills lie about the 

 western bases of both mountains, but it is noticeable that those near 

 Mt. St. Helena possess a much more prolific and rich (and more 

 characteristically coast) vegetation than the valleys and low hills 



* Erythea, I, 186, a catalogue of 156 species. 



