u8 C. H. GORDON 



the formation is placed just below the main limestone and the blue 

 shale series, the line marking the boundary with the Cisco coincid- 

 ing approximately with the east line of Shackelford County. 



The Cisco. — Below the "Albany," and outcropping to the east of 

 that formation, is the Cisco, which is composed of sandstones and 

 shales, with some conglomerates and two or three beds of coal. 

 Occasional beds of limestones occur in the lower part of the forma- 

 tion and again near the top. Coal outcrops along the Salt Fork 

 of the Brazos River west of Graham in Young County, and else- 

 where to the northeast and southwest. Some of the beds of coal 

 are associated with limestones, in one case a thickness of two or 

 three feet of limestone resting directly upon a bed of coal. The 

 conglomerates consist of sub-angular fragments of flinty blue lime- 

 stone and chert cemented together by a ferruginous sand. Nodules 

 and hollow concretions of limonitic iron ore are common. These 

 conglomerates have been recognized at two different horizons and 

 in widely separated localities. Their exact relations, however, 

 have not been clearly defined. In Stevens County the clays are 

 mostly blue and yellow. Limestones appear at intervals, but these 

 thin out northward, while the clays show a corresponding increase 

 in development. 



Relation of the "Albany" to the Wichita. — When traced northward, 

 the limestones of both the "Albany" and Cisco formations diminish 

 in thickness, while there is a corresponding increase in the inter- 

 vening beds of shale. In the case of the "Albany" the limestones 

 show also a change, becoming more earthy and irregular in their 

 texture, and some of the beds passing into gray indurated clays. 

 The few limestones in the upper part of the Cisco formation dis- 

 appear entirely in the northern part of Young County. Along 

 with this change there is an increasing development of red clay, 

 alternating with the blue. The massive beds of limestones con- 

 stituting the upper part of the "Albany" along the Clear Fork in 

 northwestern Shackelford County and in western Throckmorton 

 County were traced northward as far as Beaver Creek in eastern 

 Wilbarger County. They appear in more or less continuous 

 exposures as far north as Seymour, north of which they are covered, 

 but are again exposed, greatly diminished in thickness on Big 



