NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 47 



colating waters charged with CO^. That some such action has frequently 

 taken place in the Red Beds of Permian and Triassic age is very probable, 

 for the masses of red clay and shale are frequently streaked with green along 

 the line of larger or smaller cracks and as frequently mottled with green 

 spots where slowly moving waters may have encountered some slight excess 

 of carbonaceous material and so reduced the iron. In such cases, however, 

 the mottling and streaking are very pronounced and the action is easily 

 recognized. No trace of it can be seen in the white clay under discussion, 

 which is entirely free from any trace of ferric iron. 



That each advance of the sea was short lived is shown by the thinness 

 of the limestones, and that the increase in humidity was due entirely to the 

 presence of the sea is shown by the fact that the deposits immediately above 

 the limestone layers are nonmarine red clays and shales. 



Though the conditions outlined are typically shown on the south side 

 of Godlin Creek, they may also be observed in other places, to the north 

 along Hackberry Creek and in the breaks of the Big Wichita, i.e., wherever 

 the Beaverburk limestone shows. The same sequence is repeated several 

 times. In one place the clays below the limestone (the limestone in this 

 exact locality having been removed by erosion) are filled with plant remains, 

 Estheria, some remains of insects, and bones of small vertebrates. 



It is notable that the red clays which lie between the layers of limestone 

 and the layer directly above the highest limestone are filled with hard concre- 

 tions of impure, nodular calcite, endless in variety of form and composition, 

 and the calcite has associated with it sand, mud, iron ore, etc. 



It is safe to assume that between the limestone depositing stages of the 

 Clear Fork were periods of greater aridity, when the sea had withdrawn 

 and concentration of the waters was sufficient to induce a high calcium- 

 carbonate content, but not great enough to cause the deposit of calcium 

 sulphate, or salt, except locally, where restricted pools were evaporated to 

 the point of saturation. That the aridity did not progress to a point pro- 

 hibitive of life is shown by the frequent occurrence of vertebrate fossils in 

 the concretions. It seems probable to. me that certain of the impure lime- 

 stone beds were, in part at least, deposited from concentrated waters without 

 the action of organisms, for many of them are devoid of marine fossils, and 

 in certain layers east of the Seymour- Vernon road, near the Big Wichita 

 River, the upper surface is marked by sun-cracks, a condition that could 

 only occur in an exposed and drying mass of mud. 



Barren^ makes the following remarks about the formation of mud-cracks 

 in hmestones: 



"Mud cracking in chemical sediments, that is, in limestones, must, however, 

 be distinguished in significance from the cracking in claystones. Limestones are 

 carried in solution and their development requires a comparative absence of sand 

 and clay, the mechanical deposits carried by river s and by waves. The solutions 



» Barrel!, Amer. Jour. Sci., vol. 36, p. 438, 1913. 



