NORTJT AMERICA AND THEIR VERTEBRATE FAUNA. 45 



metallic copper have been found in the clays near Enid, Oklahoma. These 

 occurrences, however, may be due to mere incidents in a general history.* 



EVIDENCE OF CLIMATIC CONDITIONS IN CLEAR FORK TIME. 



To the west of the road running south from Dundee, approximately 

 along the east line of Baylor County, the beds above the Wichita show a 

 decided change in character. There is a much larger proportion of blue and 

 gray clays, the limestones appear, and there is a change in the character of 

 the conglomerates and coarse sandstones. The pebbles of the latter are more 

 quartzitic, or contain a larger proportion of fragments of igneous rocks. 

 Aside from the limestones, the beds retain the discontinuous character and 

 the pronounced cross-bedding. 



The lowest Hmestone is impure, earthy, whitish on fresh fracture, but 

 weathering to a rusty brown on exposure. It is not over 6 to 8 inches in 

 thickness, and breaks up into small blocks which, because of its superior 

 resistance to the soft clays above and below, determine the presence of a 

 shelf or broad terrace on the south side of the Godlin Creek, south of Fulda 

 and Maybelle, which may be traced even to the Big Wichita, where the 

 blocks are larger. This limestone, with marine fossils, clearly indicates the 

 extension of the sea over the region, probably an extension of the "Albany" 

 sea from the south. The invasion of this sea, with its fauna of marine 

 invertebrates, Myalina, Naticopsis, Nautilus, etc., was preceded by the depo- 

 sition of 6 to 8 feet of a light blue or white sandy elay, with a considerable 

 calcareous content, which is sharply defined from the red clay below and 

 the limestone above. The layer is fairly persistent, and is found just below 

 the limestone wherever the latter occurs. The white clays do not weather 

 brown upon exposure, indicating a very small content of iron, if any. This 

 means one of two things: either the clays were deposited under conditions 

 which permitted a thorough leaching out of the iron, or they were derived 

 from a region in which there were no iron-bearing minerals. The latter 

 possibility seems the least plausible. In the first place, the origin of the 

 sediments must have been at a considerable distance — the Wichita Moun- 

 tains to the north or the precursors of the Rockies to the west. And certainly 

 the character of the rocks of the central igneous cores of these masses did 

 not fluctuate. It is far more probable that the sea of "Albany" time, ad- 

 vancing toward the north and west over the semiarid coast, did not reach 

 to the mountains, but did go far enough to produce a decided effect upon 

 the humidity, and so induced a heavier rainfall, and, consequently, a heavier 

 growth of vegetation. Plant remains have not been discovered at any point 

 very far east of the first outcrop of the limestones.'' The vertical movement 



» Clark, Data of Geochemistry, 2d ed., p. 627; Haworth and Bennett, Bull. Geological Society Amer., 

 vol. I-', 1900, p. 2; Schniitz, Trans. Amer. Institute Mining Engineers, vol. 26, 1896, p. loi. (Impregnations 

 of copper ill fossil wood in the Ti'xas Permian.) 



''See David White, The Character of the Fossil Plant Giganlopleris Schenk, and its Occurrence in 

 North America, Proc. U. S. Nat. Mus., vol. 41, 1912. 

 4 



