26o REVIEWS 



Stratigraphy of the Pennsyhanian Formations of North-Central 

 Texas. By F. B. Plummer and R. C. Moore. University 

 of Texas Bulletin 2132, 1921. Pp. 237, pis. 27, figs. 19. 



This work is an important contribution to the literature of American 

 stratigraphy. Its pubhcation was made possible through the officers 

 of the Roxana Petroleum Corporation who were generous and far-sighted 

 enough to recognize that the benefits to science resulting from the presen- 

 tation of these facts to the geological profession outweigh any possible 

 detriment to their own interests. 



The Pennsylvanian rocks of north-central Texas occur as two great 

 inliers which occupy about 7,000 square miles. Because of their isolation 

 from the classic Mississippi Valley section their study has been long 

 delayed, the only earlier publications dealing essentially with their stratig- 

 raphy having been written by Tarr, Cummins, and Drake in the early 

 volumes of the Geological Survey of Texas. Recently the discovery of 

 the great petroleum resources of the region has stimulated geologic 

 investigation. 



The Pennsylvanian sedimentation in northern Texas began with the 

 deposition of the petroHferous limestone and carbonaceous shale of the 

 Bend group. At the end of this first epoch there was an uplift with 

 folding which resulted in erosion. Then followed thick beds of sand 

 and gravel interbedded with clay making up the Strawn group. These 

 coarse sediments were succeeded largely by the calcareous oozes and marls 

 of the Canyon group. During the latter part of the period there was 

 a long epoch of oscillating levels of the sea during which beds of clay, 

 sand, and limestone were deposited in alternating succession forming 

 the Cisco group. 



Of especial interest are the authors' conclusions with regard to the 

 Bend group.* On account of its economic importance as a source of 

 petroleum it has received much attention in the past, and its age has 

 been a matter of dispute. The name Bend was proposed for the black 

 shale and limestones which overHe the Ordovician beds at McAnnelly's 

 bend of the Colorado River in San Saba County. Although resting 

 unconformably beneath the coal-bearing Carboniferous sandstones, they 

 contain a preponderance of Coal Measures fossils, and were therefore 

 thought to belong to the Pennsylvanian. These beds were first referred 

 by Tarr to the Mississippian, then as a result of Cummins' work, they 

 were transferred to the Pennsylvanian system. The lowest member, 

 previously known as the Lower Bend shale, is here named the Barnett 

 shale. Many of its fossils are closely related to the Upper Mississippian 



