106 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



"The Wolfcamp consists mostly of shales which vary in color from almost 

 black to gray and greenish-gray. Interbedded with this shale are several 

 layers of limestones which are cemented shell breccias, in places conglomer- 

 atic. There are also layers of calcareous sandstones." There is possible 

 an unconformity between the Gaptank and the Wolfcamp, and the fauna 

 of cephalopods in the upper formation indicates a decided break in the 

 sequence of life between the two. 



The Hess formation consists of limestones, largely oolitic, shales, sand- 

 stones and a minor amount of conglomerate. "The color of this limestone 

 is mostly light gray. The individual beds have a uniform development and 

 can be traced for comparatively long distances. It can also be said that 

 the general aspect of these limestones resembles that of the Hueco formation 

 farther west in the State, but sufBcient collections of fossils have not been 

 made from this formation for the purpose of verifying such a correlation. 

 In its upper part, fossils are quite plentiful in certain layers. It appears 

 that the dolomitization of the limestones in this formation has proceeded 

 at quite unequal rates in different places. At the west end of the escarp- 

 ment, dolomitization is quite general. As we go away from the disturbance 

 near the igneous intrusions extending northeast from the Iron Mountain, 

 dolomitic layers appear less frequently than at the west end. The sand- 

 stones and shales of this formation are present mostly in the lower four 

 hundred feet. Most of the shale is bluish-light gray in color. The sand- 

 stones are usually free from limy material, have an open texture, and are 

 moderately fine grained. In places they show cross-bedding. The basal 

 conglomerate of the Hess consists mostly of limestone boulders, but it also 

 contains some boulders of flint and other quartz. All the underlying forma- 

 tions are represented. It varies from ten to forty feet in thickness." The 

 Hess is separated from the Wolfcamp and Gaptank by a considerable 

 unconformity. In his paper Udden says: "It is believed that the Leonard 

 is to be correlated with the Clear Fork in the west-central part of the State. 

 Perhaps it includes also the basal part of the Double Mountain, and the 

 upper part of the Albany limestones. It certainly also contains many of 

 the forms noted in the Delaware formation of Girty." He further says: 

 "Apparently there is no doubt that the Word formation belongs to the 

 Delaware deposits of Girty in the Guadalupe Mountains. It also represents 

 the main part of the Double Mountain in central Texas." 



The Tessey formation is composed mostly of unstratified dolomite re- 

 sembling the Vidrio. "It is believed that the Vidrio, the Gilliam and the 

 Tessey formations are in part the equivalents of the Capitan limestone in 

 the Guadalupe Mountains. Together they have a thickness of 3,800 feet, 

 which is more than twice the known thickness of the Capitan limestone. 

 The three formations are conformable and dip to the northwest with an 

 angle of about eight degrees." 



