SAND-HILLS, AND THEIR ORIGIN—ARTESIAN WELLS. 161 
interesting exposures of the same character are visible in other parts of the city; and in all the 3 
localities, the sections present well-defined lines of stratification, not horizontal, but inclined in 
various directions, corresponding with the direction of the wind at the time of the deposition of 
the sand. These lines are very numerous and fine, and appear to be formed partly by thin 
layers of black iron-sand, which, being heavier than the rest, is not so readily moved ; it is 
frequently seen forming the outer layer of a bank that has been swept by the wind. Blown 
sand is also found in long drifts and dunes on Point San José. It is in a state of constant pro- 
gression, passing over the point, under the influence of the wind, and falling into the water on 
the opposite side. Some large drifts are found at that place, and the grains of sand are 
unusually coarse. The surface of one of these drifts, when the wind is blowing hard, presents 
& curious appearance ; the sand sweeps along in a constant stream, which does not rise more than 
one or two feet from the surface, and when the light strikes upon it, it produces a peculiar 
halo, enveloping the drift. The same peculiar ripple-marks that are so well shown in the beds 
of streams and on the sand-hills of the Desert, are developed here in the most beautiful manner ; 
they are seen on the broad, rounded surfaces of the hills in all directions. 
Most of the hills in the city and its vicinity, where they were partly sheltered from the wind, 
are, or were, covered with a thick growth of dwarf trees and shrubs, (chamisal,) which prevented 
the wind from acting upon their surfaces and removing the sand. 
It is impossible to determine, with any accuracy, the ages that must have elapsed since this 
sand began to accumulate in Happy Valley. The progress of such hills is not uniform and 
constant, for, under certain circumstances, they remain stationary for long periods. Whenever 
the vegetation is removed, or a cutting is made, and the wind is allowed to act upon the sur- : 
face, or to strike a hill in a new direction, the motion of the sand is rapid, and a large hill is 5 
۱ soon carried away and piled up in a protected place, where the sand remains, secure from further 1 
۱ violent action. 
The Pacific coast presents many favorable opportunities for studying the phenomena of drifting 
sand and the formation of dunes. Perhaps no point is more favorable than that partly described— _ 
the sand-beach and dunes of the San Francisco peninsula. The sand of the beach is constantly 
acted on by the wind, and is thrown into hillocks of various forms and magnitude. The 
Observer may, in an hour's time from the city of San Francisco, place himself in the midst of 
this desert-like expanse, and, having viewed the production of sand-hills and drifts, he may, as 
he returns, study their internal structure and curvilinear stratification in the numerous sections * 
of the hills along the streets. 
E 15 m doceo Cad M Kc e E vga opc f 
ARTESIAN WELLS. 
Artesian borings for water in the city of San Francisco have become so numerous within three 
years, that it is almost impossible to ascertain their number and localities. Water appears to 
be found in all parts of the city around the hills, and generally at a depth of not more than one 
hundred and fifty feet; but the depth to which the borings extend varies with the locality. In - 
Happy Valley, and towards the Mission, the borings are generally successful at a depth of fifty 
to seventy-five feet, the water rising to the surface. In that part of the city north of California 
street, the depth of the wells increases ; one at the corner of California and Montgomery streets 
being eighty-five feet deep, and at Montgomery block one hundred and sixty feet. Another, 
' between Clay and Merchant streets, is one hundred and forty-two feet. The depth to which 
21F 
