Geology of Albuquerque, N. M. — Herrick. 33 
found reposing on the top of these flows, and as it seems 
necessary to seek some explanation of the superposed marl, 
we must probably look for some later agency to account for 
such dams. Perhaps flooded conditions of affluents below 
may give us the clue. It will be necessary to correlate the 
above described facts with the conditions existing in the head- 
v.aters of the Rio Grande before all the elements in the prob- 
lem can be fully understood, yet it is not hard to see that in 
a general way the record is of a river whose upper tributaries 
were under the influence of the permutations of the Glacial 
period. 
II. The Islet.\ Volcano and the Paria Mesa. 
In the valley of the Rio Grande in New Mexico is situated 
the ancient pueblo of Isleta, well known through the writings 
of Lummis, who lived there for some years while studying the 
native races. This village is about twelve miles south of Al- 
bucjuerque in the flood plain of the present river, above which 
it is raised upon what may have been a natural eminence of 
no great hight but which has been added to by accumula- 
tions of unnumbered generations. Although the pueblo is 
modernized to a great extent it is still inhabited bv the same 
race as at the earliest known date, and these Indians eke out 
their livelihood, derived from the fields and orchards in the 
vicinity, by the sale of pottery and trinkets which the squaws 
offer to the travelers on each passing train. 
It is not with the village nor its inhabitants that this paper 
is concerned, but rather with the interesting geological en- 
virons. The Rio Grande is now a sluggish stream as muddy 
as the Missouri and nearly as changeable within the narrow 
limits of the recent gorge. But the valley is full of evidence 
that the river was not always the comparatively tame and in- 
effectual irrigation purveyor it now appears. The descrip- 
tion of the valley deposits is given elsewhere, and it is only 
necessary to say here that the broad valley was at one time 
filled to the hight of about 350 feet above present water level, 
and data are yet wanting to indicate how much deeper fluvia- 
tile deposits may extend. At least three divisions in the river 
bluffs have been identified. The base of this "Rio Grande 
series," so far as known, is a thick bed of loess or fine detritus 
