20 RAYMOND C. MOORE AND FREDERICK B. PLUMMER 



limits of the Strawn, Canyon, and Cisco in the area studied by him, 

 designating definite stratigraphic horizons at the top and bottom 

 of each. Many of the subdivisions defined by Drake are employed 

 in the present classification, but in a number of cases it has seemed 

 necessary to depart from his usage and to apply appropriate 

 geographic names for units to which he gave merely descriptive 

 names, as "Cherty" or "Coral" limestone. 



In addition to the investigators whose work has just been 

 mentioned, a considerable number of geologists have reported 

 studies of value on various portions of the Texas Carboniferous 

 beds. Among these may be mentioned Hill,^ Gordon,^ Paige,^ 

 Udden,4 Girty,^ Moore,^ and Plummer.^ All of these investigations 

 have been studied carefully by the writers in connection with the 

 present work. 



Recent investigations. — In December, 1916, the geologists of the 

 Roxana Petroleum Corporation began the systematic mapping of 

 the surface and structural geology of the northern portion of the 

 Pennsylvanian area in Texas. As the work progressed the maps 

 were fitted together and the data slowly compiled for a new, 

 detailed, geological map of north Texas. At present almost the 

 entire area of the Pennsylvanian outcrops has been mapped, the 

 outcrops of all the principal limestones and many other beds having 

 been traced by means of plane table and alidade. Several hundreds 

 of geological sections have been measured and carefully described. 

 Fossils have been collected from most of the stratigraphic divisions, 

 those from some horizons having been studied in detail. Finally, 

 much information has been obtained from the records of numerous 

 wells over a large area in north Texas which have been drilled 

 deeply into or through the Pennsylvanian. 



1 R. T. Hill, U.S. Geol. Surv., Twenty-first Ann. Rept. (1901), Part VII. 



2 C. H. Gordon, U.S. Geol. Surv., Water Supply Paper 276 (1911). 



3 Sidney Paige, U.S. Geol. Surv., Geol. Atlas, Folio 183 (191 2). 



4 J. A. Udden, Bur. Econ., Geol., and Tech., Bull. 44. (1916). 



s G. H. Girty, Bull. Amer. Assoc. Petrol. Geol., Vol. Ill (1919), pp. 71-81. 

 ^ R. C. Moore, Bull. Amer. Assoc. Petrol. Geol., Vol. Ill (1919), pp. 216-52; G. H. 

 Girty and R. C. Moore, Bull. Amer. Assoc. Petrol. Geol., Vol. Ill (1919), pp. 418-20. 

 7 F. B. Plummer, Bull. Amer. Assoc. Petrol. Geol., Vol. Ill (1919), pp. 132-50- 



