248 ENVIRONMENT OF VERTEBRATE LIFE, ETC. 



ring in rainy seasons alternating with dry seasons. Barrell says^ of the 

 significance of the appearance of red sediments : 



"Turning to the climatic significance of red, it would therefore appear both 

 from theoretical considerations and geological observations that the chief condi- 

 tion for the formation of red shales and sandstones is merely the alternation of 

 seasons of warmth and dryness with seasons of flood, by means of which hydra- 

 tion, but especially oxidation of the ferruginous material, in the flood-plain 

 deposits is accomplished. This supplements the decomposition at the source 

 and that which takes place in the long transportation and great wear to which 

 the larger rivers subject the detritus rolled along their beds. The annual wetting, 

 drying, and oxidation not only decompose the original iron minerals, but com- 

 pletely remove all traces of carbon. If this conclusion be correct, red shales or 

 sandstones, as distinct from red mud and sand, may originate under inter- 

 mittently rainy, subarid, or arid climates without any close relation to tempera- 

 ture and typically as fluvial and pluvial deposits upon the land, though to a 

 limited extent as fluviatile sediments coming to rest upon the bottom of the 

 shallow sea. The origin of such sediment is most favored by climates which are 

 hot and alternately wet and dry as opposed to climates which are either con- 

 stantly cool or constantly wet or constantly dry." 



The question of the greatest climatic significance in the constitution of 

 the red beds of Permo-Carboniferous time is whether the color is original or 

 has been produced secondarily by a dehydration of hydrated oxides of iron 

 by pressure or chemical change. That the color is a primary one due to 

 deposition of the ferric oxide as such with the sandstones and shales is 

 fairly certain. Observations by Case and by Baker have been reported 

 upon this subject. 



Case^ says of the beds in Texas and Oklahoma : 



"We may be certain that the red clays of Texas, with their ferric oxide, were 

 deposited in the sea, or other bodies of water, in the condition in which they now 

 occur, and are not due to subsequent dehydration or decarbonation, because 

 (i) the color is uniform throughout; (2) because there is a solidity and density 

 in the clays, and a lack of filled seams and veins, which would be impossible 

 after such changes, which involve a decided increase in volume; and (3) because 

 the red color transgresses into the limestones and sandstones with marine fossils." 



Baker,^ writing of the same region, found that the following facts 

 indicated a non-arid condition of 'Red Bed' origin: 



"i. 'Red Beds' are not being formed to-day in any desert region. On the 

 contrary, they are being formed under conditions of warm, moist climates in the 

 southern temperate and tropical regions, as maturely weathered residual soils. 

 They are being formed, for example, in such regions as the southeast Texas Gulf 

 Coastal Plain, the Great Valley of the Southern Appalachians, and as laterite in 

 the subtropical and tropical regions. 



' Barrell, Joseph, Relations Between Climate and Terrestrial Deposits, Jour. Geol., vol. 

 XVI, p. 292, 1908. 



' Case, E. C, The Permo-Carboniferous Red Beds of North America and their Verte- 

 brate Fauna, Carnegie Inst. Wash. Pub. No. 207, p. 43, 1915. 



' Baker, C. L., Origin of Red Beds, University of Texas Bull. 29, p. 3, 1916. 



