Lazvs of Nc7i' Mexico Mountain Ranges. — Herrick. 309 
claim have never beeen published and I venture to offer the 
evidence from a section directly eastward from the Socorro 
mountain, beginning at the river. In the ascent of one of the 
large arroyos opening upon the flood plain opposite the School 
of Mines one may see the relations very clearly and the sec- 
tion given supposes the bed of the arroyo exposed in one sec- 
tion running east and west. 
For the first three miles and more the red and grey Tertiary 
beds rise on either side to a hight of some 50 feet. Their ma- 
terials are loam and gravel at first, with sand-bar and local 
gravel beds at times. For the most part, the stratification is 
very true and persistent, contrasting, in this respect, with the 
Pleistocene beds near the river. 
The dip is to the west and is slightly greater than the in- 
clination of the arroyo. It may be as much as 25 to 50 feet per 
mile. Toward the east, as one approaches the foot-hills, the 
materials become coarser and consist of granitic pebbles, frag- 
ments of Carboniferous and red-bed strata. Abruptly the strata 
of sand and coarse pebbles abutt upon the irregular surface of 
the granite which is evidently smoothed by water-erosion, and 
the parts of the strata immediately adjacent to the granite are 
filled with conglomeritic masses of the granite to the exclusion 
of the other ingredients. 
East of the first exposure of granite is a basin-like interval 
in which lies a portion of the lower beds of the same series ex- 
posed in the Socorro and Limitar mountains. These lower 
beds dip to the east and repose on the granite. They consist 
of prevailing quartzytes and sandy shales with beds of limy 
shales and sandy limestones of a peculiar character. There can 
be little doubt that this series is the same as that found at the 
lowest horizons in Socorro mountain, below the large quartzyte 
beds. The exposure is imperfect and very incomplete at that 
place, while here it is well shown. The eastern wall of the 
basin referred to is formed by an abrupt exposure of granite 
rising to over one-hundred feet above the arroyo. The strata 
lap at a high angle against this granite boss, while on the east- 
em side they are repeated and the whole magnificent series of 
Coal-Measure and Permo-Carboniferous rocks is within easy 
reach and in uninterrupted sequence. This series will be de- 
scribed in detail elsewhere, but it will be of interest to show 
