30 The America?i Geologist. July, i89s 
University campus, but further south it is quite conspicuous 
as a white band near the summit of the blufifs for many miles. 
The following is the partial analysis made by Prof. R. W. 
Tinsley, chemist of the university. 
SiO,.... 26.53 
FcgOg 1.20 
CaCo^ 64.47 
It will be a matter of considerable local interest to deter- 
mine the conditions under which such a marl could have been 
formed. If one could find evidence of a dam below Albu- 
querque, which at the time when the flood plain had reached 
its highest point could have formed a great lake or estuary, 
it could be supposed that highly carbonated water from the 
limestone areas to the east may have spread over the bottom 
this rather uniform layer of calcareous material. The forma- 
tion of such lakes or quiet spots on a small scale in the river 
valley has other illustrations. Or one might be tempted to 
think of wide-spreading flows of volcanic waters charged with 
a material sedimented out on cooling. That the marl is not a 
purely local deposit is proven by its occurrence on both sides 
of the river. 
Beneath the marl is a considerable band of gravel and 
rounded stones of variable size. The materials are chiefly 
quartzytes, gneisses and granites, evidently the debris from 
the metamorphic series already mentioned, though fragments 
of andesytes, trachyte, rhyolyte and basalt are also found. 
In some places the gravels on the east side of the river con- 
tain scoria and basalt evidently of the age of the recent cones 
of the west side of the river, suggesting an extension of those 
flows to the east of the present river. And as fragments of 
petrified wood occur with them we may also conclude that 
the underlying materials in this place were of the same age 
as where exposed elsewhere, — namely Cretaceous. The thick- 
ness of these gravels may vary from two to twenty or more 
feet. Beneath these appears a sandy loess passing into clay 
sometimes carrying fragments of undecayed wood. The 
depth of this stratum is as yet but imperfectly known, but it 
is eminently characteristic and may'be recognized everywhere 
in the immediate blufTs of the river. In some places it has a 
