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"Fossils are extremely abundant in the septarise and nodules, and as far as I have been able to learn they belong to hitherto undescribed species. From the collections of Dr. G. G. Shumard I have been able to characterize the following: Ammonites swallowi, A. inequiplicatus, A. meekianus, A. graysonensis, Ancyloceras annulatus, Scaphites vermiculus, Baculites gracilis, Cy. therea lamarensis, Tapes hilgardi, Gervilia gregaria, Nucula haydeni, Panopæa subparallela, Corbula graysonensis, O. tuomeyi, Inoceramus capulus, and Inoceramus sp. nov. Fossil wood is also common at several of the localities visited."
Dr. B. F. Shumard, however, almost inextricably mixed his brother's results in his generalized section of Texas rocks, and I am inclined to believe that some of these species belong to the Eagle Ford clays, and are so placed in the Check List.
THE STRATIGRAPHY OF THE COMANCHE SERIES IN GENERAL.
From the foregoing facts it is evident that the Comanche series possesses a well defined lithologic and stratigraphic history. Its lower division is essentially sandy, but becomes less and less so and more calcareous as the bottom upon which they were laid down subsided.
The alternating beds of the Basal subdivision of the Fredericksburg clearly show a deeper sea condition of origin than the Trinity, but not as deep as the chalk of the Comanche Peak and Caprina limestone subdivisions. After the latter there is a hiatus in our knowledge, but the Washita division reveals an elevation of the ocean's bottom as slow and positive as is the subsidence recorded in the other basal divisions. In brief, there is recorded
- (1) a long continued subsidence, during which nearly one thousand feet of deepening sediments were laid down;
- (2) a long continued deep sea condition in which four or five hundred feet or more of chalks were deposited;
- (3) an elevation in which from three hundred to five hundred feet of shallowing sediments were deposited (the Washita division).
The lithology of the Comanche series is predominantly calcareous and is marked by several essentially chalky horizons.
There are also magnesian and arenaceous beds, but these are modified in color and appearance by the predominance of the accessory chalky matter. In color the tint is chalk white, yellow, cream-colored, and occasionally the white rock weathers into a dark grey, and not even in a single case are these rocks concretionary as recently recorded, unless it is in a few feet of the Denison beds above mentioned.
"A recent writer has alleged concerning these rocks: "I have no doubt that the 4000 feet of limestone which I found in the San Carlos Mountains of Chihuahua were accumulated on a subsiding sea bottom. Deep sea forms seem to be either wanting or very rare. I did not detect any forms from top to bottom of the series that might not have lived in comparatively shallow waters." Am. Jour. Science, Jan., 1890, p. 70.)
Am. Jour. Science, Dec., 1889, p. 443