INTERPRETATION OF ENVIRONMENTAL CONDITIONS 211 



The clays thus derived and their coloring matter — the red oxides of iron — are 

 minutely divided and when in suspension settle slowly, but little movement of 

 the water being sufficient to keep them in suspension. This characteristic 

 adapts them to long transportation. The great thickness of the Arbuckle and 

 associated limestones, and their former extent, over thousands of square miles of 

 country where they are now removed or represented only by their upturned 

 edges surrounding the mountains, seem to furnish an ample source of the coloring 

 matter and a considerable amount of clays of these low Oklahoma red beds. 

 The gabbros, red granites, and red porphyries of the Arbuckle-Wichita region 

 also contributed their share of sediment to the red beds. 



"From these observations it would appear that the sediments of the lower 

 red beds of Oklahoma were derived largely from the Arbuckle-Wichita Permian 

 land-mass and the coloring matter mainly from the solution of the limestones 

 known to have been removed from it. It also seems probable that the sediments 

 of the region studied, especially those some distance from the mountains, were 

 deposited in very shallow turbulent water, or vast tidal beaches, inimical to life 

 of all kinds, since they are void of fossils or even carbonaceous matter." 



Baker,^ writing more particularly of the Texas beds, says: 



" In Texas, Oklahoma, and Arkansas, early Pennsylvanian marine sedimenta- 

 tion was followed by mountain-making movements in the Ouachita Mountains 

 region of Arkansas and southeastern Oklahoma, and in the Central Mineral 

 (Llano-Burnet) region and the trans-Pecos country (Marathon, Van Horn, and 

 El Paso regions) of Texas. The newly-formed mountains were rapidly eroded 

 and a large part of the mountain region resubmerged beneath the sea in later 

 Pennsylvanian time. In the western trans-Pecos region a later Pennsylvanian 

 limestone nearly a mile in thickness was deposited and in the Marathon region 

 shales and limestone covered the much-eroded, closely folded earlier Pennsyl- 

 vanian and early Paleozoic rocks. In north-central Texas later Pennsylvanian 

 sedimentation began with sandstones, conglomerates, and shales, and was fol- 

 lowed by shales and limestone. The land-derived sediments seem to have been 

 derived from lands to the east and southeast, and for this reason it is believed 

 that the mountains of the Central Mineral region were then more or less con- 

 tinuous with those of southeastern Oklahoma and west-central Arkansas, and 

 perhaps stretched westward to the Marathon Mountains. * * *" 



"The Pennsylvanian sea of north-central Texas was never very deep and its 

 waters were seldom free from sand and mud brought to it from land areas on 

 the south and southeast. It \vas only near the close of the period, and then only 

 in the southwestern part of the region, that the sea-waters became fairly clear 

 from land-derived sediments. The coal beds, found in the Strawn and Cisco 

 formations, were probably formed in regions of coastal swamps, the surfaces of 

 which lay very close to sea-level. Comparatively rapid oscillations of sea-level 

 must have sometimes taken place, because we find beds of coal directly overlain 

 by limestones containing abundant marine fossils. 



"We may draw for ourselves a fairly vivid picture of later Pennsylvanian times 

 in north-central and west Texas. To the westward lay a great sea with clear 

 waters abundantly teeming with marine animals. On the south and southeast 

 was the land of mountain ranges which came into existence earlier in the Penn- 

 sylvanian. Between this land and the western sea was a low foreland and 



^ Baker, C. L., Origin of Texas Red Beds, University of Texas Bull. 29, 1916. 



