Geology of AUmqiicrqiic, N. M. — Hcrrick. 31 
clayey consistency, while more often it is composed of fine 
grains of sandy material. About Albuquerque it is in request 
as a "molding sand," for which purpose it is well adapted. 
It is plain that this series, which we shall designate as the 
"* Rio Grande loess," must have been deposited during a 
period of abundant but sluggish flow. The great extent and 
the horizontality of the series afford proof of these sugges- 
tions. The loess seems to repose upon the Cretaceous of the 
immediate valley of the river. The original inclination of the 
valley must have been greater than at the close of the loess 
period, for only ten miles above the city of Albuquerque the 
obliquely tilted sandstones of the Cretaceous appear in the 
river bed. It appears probable that in many places at least 
there is a stratum of coarse material between the loess and 
the bed rock, though the only direct evidence we have is from 
the reports of well-diggers who report a stratum of "cobble 
stones" as the water-bearing horizon at a depth of 350 feet 
upon the mesa three miles east of the University campus. 
It may be assvmied that the river silted itself up during the 
period of quiet represented by the loess. If so, the re-exca- 
vation of the channel must have followed immediately, for. 
as above stated, the next number of the series, the " Rio 
Grande gravels,'' is an exceedingly variable quantity. It is 
a coarse or moderately fine deposit of the most diverse mate- 
rials. Among these the granitic and quartzytic fragments 
from the neighboring mountains may be said to predominate, 
yet there are localities where the entire deposit is composed of 
volcanic scoriae. In a previous paper the writer has described 
the instance further down the river where an isolated basin 
lias been filled with floating pumice, which deposited by its 
own abrasion the so-called Socorro tripoli. A somewhat 
similar instance has since been found about nine miles north 
of Albuquerque where a large deposit of the same character 
may be seen from the train. Large quantities of the dark ba- 
salt of the local flow^s along the valley are noticed everywhere 
in these gravels together with rounded fragments of andesyte 
and trachyte derived from the older eruptives penetrating the 
stratified series of the valley margin. The upper surface of 
the loess is everywhere deeply eroded and in the irregularities 
so produced are deposited the coarser elements of the gravel. 
