3ic» The .American Geologist. ^^^y- '^^^*- 
that the base of this exposure is certainly of Coal Measure age. 
Resting- on the granite is a quartzyte, as usual, but above it and 
locally well-developed, is a bed of blue shale and fire-clay that 
has been extensively mined by the Socorro Fire Clay Co. From 
these beds were collected the lepidodendrids figured in the Bul- 
letins of the University of New Mexico, Vol. II, Plate VII, 
figs. I to 4. These were recognized as Coal Measure species, 
though they may prove new, but nothing definite was known 
as to their position with reference to the known horizons. But 
in this locality there are superposed upon these shales in un- 
broken succession over 200 » feet of alternating sandy shales, 
sandy limestones, and quartzytes or sandstones, in which is 
preserved an abundant fauna of undoubted Coal Measure hab- 
itus. (Plate XVI.) 
This sandy series corresponds in position to what we have 
called in Bernalillo county the "Sandia series'' of the Carbon- 
iferous and it is immediately followed in both places, as well 
as at Socorro mountain, by a series of shaly limestones afford- 
ing the most complete Coal Measure fauna yet observed in 
Nev/ Mexico. The transition into the Permo-carboniferous is 
affected very gradually through several hundred feet of mas- 
sive grey limestones with few quartzyte beds. 
The above observations acquire greater significance when 
we remember that further southeast, in the Sacramento moun- 
tains, the writer has found a well defined Burlington series be- 
neath the Sandia strata and that in the extreme southwestern 
part of the territory the Burlington and strata evidently older 
(probably Devonian )are known to occur. There is a very 
general belief that the lower 100 feet in the Magdalena range 
may be older than the Coal Measures, though the bulk of the 
rocks are late Carboniferous and Permo-Carboniferous. The 
writer has seen no paleontological evidence for the Sub-Car- 
boniferous in the range and by reason of the analogy widi the 
Socorro mountains and other adjacent regions where metamor- 
phism is less destructive to fossils, has regarded the whole 
limestone series as probably as late as the Coal Measures. Sub- 
Carboniferous crinoids, however, in two cases, are said to have 
been found in the ore-bearing horizons and more light may be 
eventually expected on this point. 
