162 
GEOLOGY. 
the borings are carried, increases from the base of the hills towards the hay, and many of the 
wells are bored down through the salt water of the hay. 
None of these Artesian borings have been carried downwards into the sandstone strata ; they 
only pierce the superficial drift or alluvium. Several veins or strata of water are generally 
found ; and when the borings first commenced, an overflow was generally obtained. 
The formations that are successively passed in boring, are sands and clays, and the water is 
found to rise from the sandy strata alone. Towards the Mission, a very heavy and thick forma¬ 
tion of blue clay is met with, containing roots and leaves partly decomposed, and giving off a 
disagreeable odor. This clay is over fifty feet thick, and water is found below it. The configu¬ 
ration of the underlying strata of sandstone and shale is highly favorable to the success of 
Artesian borings in the overlying drift or detrital accumulations. It is possible that water 
could also be obtained from the slaty layers between the compact sandstone strata; but the 
drilling of the rock would be attended with great expense, and it is questionable whether the 
formation is not so compact and dense as to prevent rapid infiltration, or a subterranean flow of 
water. 
Some of the wells in the city are eighteen inches in diameter, and cased with cast-iron pipes ; 
others have a simple and temporary lining of sheet-iron like a stove-pipe. The cost of the 
wells, complete, with the ordinary lining, is about four dollars per foot. 1 
At the villages of Santa Clara and San Jose, Artesian borings have been entirely successful. 
At San Jose, during the past winter, (1853,) the earth was bored to a depth of seventy-eight 
feet, through the fine alluvial clay of that valley. At that depth, the auger suddenly dropped 
into a stratum of water and sand, and, on being withdrawn, the water followed it to the sur¬ 
face and overflowed freely. The column has since been raised several feet by the addition of 
pipes, and an elevation sufficient to irrigate the surrounding lands is attained. No diminu¬ 
tion in the volume of water discharged has yet been observed ; but several other wells are about 
being sunk, which will perhaps reduce the quantity. 
Several other wells have been constructed with satisfactory results. One of the borings was 
remarkably successful; at the depth of about seventy-five feet, a rush of water to the surface 
took place, and has continued to overflow without diminution. Such is the pressure and force 
with which this water rises, that it has been found difficult to control it and prevent it from 
overflowing the adjoining grounds. Another is reported to have been sunk to the depth of two 
hundred and twenty-five feet, and to yield seventy-five gallons a minute. The drainage from 
the different wells forms a brook large enough to drive a saw-mill. The success attending the 
Artesian borings in that alluvial valley is so general, and the advantages obtained are so great, 
that they are becoming very numerous. The Aftesian wells can also be constructed at an 
expense that of ordinary wells. 
1 I am indebted for many of these facts to Mr. Hopkins, who has heen engaged in boring wells in San Francisco for two 
years past. (February, 1854.) 
