Art. IX.] Herrick-Johnson, Geology of the Albuquerque Sheet 183 
ward being low hills at Bernalillo and bluffs perhaps seventy-five 
feet high at the mouth of the Tijeras arroyo. At the north the 
Tertiary sands emerge from under the Pleistocene gravels, as 
about Bernalillo, but to the south these exposures disappear. A 
shoulder of schist from the granitic series forming the base of 
the Sandia range is thrust into the mesa at its north-eastern cor- 
ner and about this some Tertiary elments may be detected. The 
Pleistocene deposits have been described in some detail in the 
first volume.^ In that paper the mistake was made of tentatively 
referring the stratified sands beneath the river deposits to the 
Cretaceous. It appears that these .beds must be as late as 
Neocene Tertiary though as yet no positive identification can be 
made in the absence of distinctive fossils. The lowest member of 
the river series is what we called the Rio Grande loess and this 
horizontally stratified deposit of fine silt and sand occupies the 
valley of the river as far south at least as to near La Joya. It 
contains fragments of marl which may have been derived from 
the disintegration of the Tertiary marl deposits. It is impossi- 
ble at present to decide as to the depth of the deposit but pre- 
sumably it does not extend much below the water level in the 
river. A well driven at a point rather south of east and about 
four miles from the city is 370 feet deep. The lower 25 feet is 
in a water bearing zone the foundation of which is clay. Ex- 
cept at the top the material passed through was fine grained 
loess. This depth would correspond pretty well with the level 
of the river and as no bed of clay is known in the Tertiary it 
may be supposed that this well reaches the bottom of the Pleis- 
tocene series. Another well not more than two miles east of 
town is said to have a depth of 214 feet and to pass through the 
same loose materials. The loess is well seen in the bluff of re- 
cent erosion on the west bank of the river opposite the court 
house. Here some 75 feet are exposed in a single perpendicu- 
lar wall. From the top of this bluff looking eastward there may 
be readily seen a layer of gravel about 25 feet thick which occu- 
^ The Geology of the Environs of Albuquerque. American Geologist, July 
1898. Reprinted in Bulletin Univ. New Mex., Vol. 1 . 
