112 Permian Formation of Texas. 
that the same formation has furnished lo species of fishes, ii of 
batrachians and T^^i of reptiles ; 54 species in all. 
The full thickness of the Coal-measure series in Texas is not yet 
known, its base not having been observed ; but the portion that 
has been examined reaches an estimated thickness of 1800 feet. 
The strata are generally somewhat evenly bedded, and consist of 
bluish and gray limestones, gray and ferruginous sandstones, blu- 
ish and carbonaceous shales and clays ; and several coal horizons 
are now known in the series there.* These strata have furnished 
at numerous localities, and in greater or less abundance, such char- 
acteristic Coal-measure invertebrates as the following : Terebratula 
bovidens Morton, Spiri/er cameratus Morton, Athyris subtilita Hall, 
I'roductus cora d'Orb., P. nebrascensis Owen, P. costatus Sowerby, P- 
setnireiicttlatus Martin, Hemipronites crassus Meek and Hayden, 
Myalina siibquadrata S>hnn\2ix6, Al/orisma subenneafa M. and H.,i\^/^ 
eiiiana bellistriata Stevens, Pleurotomaria tabulata Conrad, Bellerophon 
carbonarius Cox, B. percarinatus Conrad, and Macrocheilus pondero- 
siis Swallow. Many other species also have been found associated with 
those which have been just named, but the latter are quite sufficient 
to characterize the strata containing them as belonging to the Coal- 
measure series. No attempt has been made to subdivide the Coal 
measure series of Texas into upper, middle, and lower portions as 
has been done in the Upper Mississippi Valley, and they are prob- 
ably not capable of such a subdivision in this southern region. 
The Lower or Subcarboniferous portion of the system has also not 
been recognized in Texas. 
Along the western boundary of the Texas Permian, as it has been 
indicated in a previous paragraph, a series of strata, about 250 feet 
in maximum thickness, now generally known as the "gypsum-bearing 
beds " and thought by many to be of Triassic age, rests conformably 
upon the Permian. In general aspect, in a prevailing reddish color. 
and in general lithological character, except in the prevalence of gyP' 
sum in many of the layers and the somewhat greater prevalence of 
clayey material, these overlying beds resemble the Permian strata 
upon which they rest. AVith only one known exception these gyP' 
sum bearing beds have furnished no fossils. The exception refer- 
red to is the discovery by Mr. Cummins in Hardiman county, in a" 
upper stratum of those beds, of a thin magnesian layer contaming 
^ Mr. Cummins informs me in an unpublished letter that he has distinguished no 
