I. C. Russell—Subaérial Deposits of North America. 293 
A large number of wells have been bored in the Great Valley of 
California, which penetrate alternating layers of unconsolidated 
sand, gravel and clay, to depths varying from a few hundred to 
2300 feet without reaching bed rock. The deepest of these is 
situated in the northern part of the San Joaquin Valley, as I have 
been informed by Wm. Ham. Hall, State Engineer of California. 
With these measurements before us, it does not seem that an 
estimate of three thousand feet or more, for the thickness of the 
superficial deposits in many of the valleys of the Arid Region, is 
too great. My confidence in this conclusion has been increased 
by finding that the depth of superficial material in the valley of 
Great Salt Lake has been estimated by G. K. Gilbert? at 5000 o 
6000 feet. 
Physical Characters.—Typical examples of adobe may be seen in 
thousands of places in the Arid Region, where sun-dried bricks are 
being made. In every Indian and Mexican village of Arizona and 
New Mexico there are excavations where material has been obtained 
for this purpose. Many times the bricks used in the construction of 
a building are made from the earth removed in digging its founda- 
tions. At these and many other localities where the adobe is open 
to view, it appears as a fine-grained porous earth, varying in colour 
through many shades of grey and yellow, which crumbles between 
the fingers, but separates most readily in a vertical direction. The 
coherency of the material is so great that vertical scarps will stand 
for many years without forming a noticeable talus slope. The sun- 
dried bricks made from it are more durable than the escarpments 
of natural earth, and when built into walls are capable of standing 
the atmospheric conditions to which they are subjected for scores of 
years. There are buildings now in use in Santa Fé, N.M., built of 
sun-dried bricks, which, I have been assured on good authority, 
have been standing for more than a century. 
Adobe is frequently exposed in the sides of arroyos or dry water- 
courses, especially in the valleys along the eastern base of the Rocky 
Mountains from Wyoming to Mexico. At Cafon City, Colorado, 
exposures of this character are abundant, and sections from fifteen 
to twenty feet in height may be examined in detail. Wells dug in 
the same region have penetrated the adobe to a depth of forty feet 
without reaching its lower limit. At these and at numerous other 
localities that have been examined no lines of stratification could be 
distinguished, but the deposits were homogeneous throughout, except 
at times when lines of pebbles marked more or less definite horizons. 
Pebbles are most abundant near the mountains, and become less and 
less frequent as one recedes from them. At a few localities the 
adobe was seen to be traversed by small vertical tubes, some of 
which branched downward. In samples collected at Santa Fe, N.M., 
the tubes have a diameter ranging from a fiftieth to a hundredth of 
1 Physical Data and Statistics of California, Sacramento, 1886. 
2 Report on the Geology of Portions of Nevada, Utah, California and Arizona, 
in Report of Geographical and Geological Explorations and Surveys West of the 
100th Meridian, Washington, 1875, vol. ii. p. 66. 
