REVIEWS 673 
beneath it, giving, all told, some 2,500 feet to this formation and a total of 
about 4,000 feet to the whole Guadalupian section as shown at the southern 
extremity of the mountains. The stratigraphy was largely worked out by 
Richardson.t To the east, on the dipslope of the mountain, the Capitan 
limestone is wanting. An erosional unconformity is found on the Delaware 
Mountain formation upon which rests the Castile gypsum. The exposures 
of the region show 50 or 60 feet of it and a well at Rustler spring penetrated 
it to a depth of 300 feet. Upon this gypsum lies the Rustler formation 
consisting of magnesian limestones and sandstone with an average thick- 
ness of about 200 feet. To the east, and upon this, lie the Red beds. Rich- 
ardson’s interpretation of the stratigraphic succession is as follows: 
The Castile gypsum along its western outcrop lies on little knolls and valleys 
of the underlying Delaware Mountain formation, indicating an erosional uncon- 
formity. Another evidence of unconformity at the base of the gypsum consists 
in the absence of the Capitan limestone. It appears that either the gypsum was 
deposited at or near the top of the Delaware Mountain formation as a lens which 
did not extend westward to intervene between the Delaware Mountain formation 
and the Capitan limestone in the Guadalupian Mountains, or that erosion had 
removed the former southwestward extension of the limestone (the thickness of 
which is unknown) before the deposition of the gypsum. ‘The former position 
necessitates the correlation of the Rustler formation, which overlies the gypsum, 
with the upper part of the Delaware Mountain formation or the Capitan limestone. 
But there is little to support this interpretation, and it is tentatively assumed that 
the Castile gypsum and the Rustler formation were formed after the deposition 
and erosion of a part of the Capitan limestone.? 
The Red beds approach the Guadalupes closely from the north, and 
Tarr states that a thousand feet or more of sediments come in on top of the 
Capitan limestone to the north in New Mexico. Up to the present time 
the Triassic has not been reported from southern Texas and southern New 
Mexico, Lee’s researches along the Rio Grande in New Mexico and; the 
explorations of the Texas survey having failed, so far, to reveal it. So 
it would not be at all impossible that the Rustler formation pushes up the 
dipslope and over the Capitan limestone farther north, and that both lie be- 
neath the upper Red beds. However, it is not certain that this happens, and 
Dr. Girty’s interpretation of the faunas seems to be that such is not the case. 
Nevertheless the fact that the unconformity exists, that the Capitan limestone 
is unknown beneath the unconformity lying upon its natural dipslope, and 
t Bull. 9, Univ. Tex. Min. Surv., 1904. 
2 Op. cit., Pp. 43, 44. 
3 Jour. Geol., XV, pp. 52-58, 1907. 
