50 



THE SALTON SEA. 



cracks show how firmly bound the soil is by the roots of the turf-forming flora which it 

 supports. When wet, the turf and soil may be cut into blocks of suitable size, and such are 

 used for building dikes. These dikes run in some cases as dams along the tidal channels — 

 "sloughs" — of the lower parts of the marsh. In others they form the borders of artificial 

 ponds, often of extensive area. The undisturbed and carpeted soil of the marsh forms the 

 bottoms of these ponds. Into the ponds the water of the bay is pumped. Formerly the 

 pumps used were Archimedes screws driven by low sails. These used to give a curiously 

 foreign and antiquated appearance to the parts of the shore used for salt-making, but elec- 

 tric pumps have now displaced the slower wind-driven ones and rough poles and wires dis- 

 figure the marsh. 



CUMATOLOGY. 



As is well known, the climate of middle California is extraordinary. Because of the 

 decided difTerences in rainfall, temperature, clearness, humidity, and wind within short 

 distances, on account of topographical and other difTerences, general statements are diffi- 

 cult. The lack, therefore, of official rainfall and other climatological data for a given spot 

 makes accurate description of that spot the more difficult. As shown by McAdie,' the 

 mean annual rainfall increases from San Jose, near the southern end of San Francisco Bay, 

 to San Francisco about 50 per cent, being 14.88 inches at the former station and 23 inches 

 at the latter. The organisms described below inhabited the salterns near Redwood City, 

 about midway between these two points. There are no official rainfall data for this local- 

 ity, but computation from the figures in McAdie's important book and from the Annual 

 Reports of the Chief of the Weather Bureau, supplementing my own records, will throw 

 much light upon the behavior of the organisms in question and be entirely safe. Much 

 greater differences in rainfall may be found within shorter distances in this same region,^ 

 but they do not concern us. The difference in rainfall in a north-south direction is due 

 principally to the trend of the mountain chains. On them the rainfall is much greater than 

 on the valley floor. San Jose is at some distance from both chains of mountains walling 

 in the Santa Clara Valley; Redwood City is nearer the Montara Range on the west, and 

 San Francisco is upon its slopes. The annual rainfall on the Redwood marsh should aver- 

 age about 18 inches. 



Quite as significant as the smallness of the annual rainfall is the limited time of its 

 occurrence. Although this varies from year to year, with accompanying differences in 

 the behavior of all living organisms, it is generally true that no rain falls from May until 

 September. There may be no rain until November, and the season's rains may come 

 to an end early in April. Generally, the heaviest rains occur in January or even in Decem- 

 ber. The annual distribution of rain may be seen in table 20, taken from McAdie's Cli- 

 matology of California. 



Table 20. — Average rainfall, in inches, at San Francisco and San Jose, by months, for certain periods. 



The mean between these would give us approximately the rainfall at Redwood City, 

 but this calculation is unnecessary. It is evident from the table that rain falls in late 

 autwnn, throughout the winter, and in early spring; that in summer and in late spring 

 and early autunm there is little or no rain. 



» McAdie, A. G.: CHimatology of Califoniia. Bull. L, Weather Bureau, U. S. Dept. Agric, Washington, 1903. 

 • Peirce, Q. J.: The botanical aspects of Stanford University. Plant World, vol. xii, p. 245, 1909. 



