32 
The Ametican Geologist. 
July, 189« 
Fig. 1. An exposure in the suburbs of Albuquerque showing the eroded upper surface 
of the Rio Grande loess with the irregularly banded gravel reposing upon it. 
Fig. I illustrates such an instance in the banks whence mold- 
ing sand has been removed at the eastern end of Lead avenue 
in the city of Albuquerque. Not only are the deposits of 
gravel very irregularly distributed, but it appears that they are 
mostly collected in the centre of the valley or near the pres- 
ent river bed. It would seem safe to assume that these 
gravels represent a torrential period in the history of the river 
and that accordingly this was a period of active erosion, of 
numerous changes in the river, and corresponding irregularity 
of deposition. The river must have stood at times at a high 
level, and it may be that this was a time of breaking away of 
old barriers. The loess must have been high enough to have 
caused the river to flow over some of the recent lava sheets 
of the valley, as is shown by the abandoned channels at vari- 
ous places in the lower course of the river. In fact, one is 
almost irresistibly reminded of the conditions in glaciated re- 
gions, where old river courses are continually being revealed. 
Yet in these cases it would seem that the direct agency of ice 
is excluded. One such instance is to be described beyond, 
while a still more extensive occurrence in the neighborhood of 
La Joya may form the subject of a later contribution. It was 
at first thought that the river had been dammed at these 
points by flows from the adjacent craters, but as further exam- 
ination seemed to show that the flows were older than the 
loess and certainly older than the gravels which are, in places. 
