Fauna and Stratigraphy of the Stormberg Series. 471 



is due to the presence of ferric oxide. A grey or green colour sig- 

 nifies a low proportion of ferric oxide, and usually a preponderance 

 of ferrous over ferric compounds". Tomlinson considers the theories 

 which propose respectively that the iron has subsequently been in- 

 troduced into the sediments from igneous magmas, and that it is due 

 to subsequent deposition from meteoric water; neither of these theories 

 lias much evidence in its favour. Wherever intrusions have affected 

 Red Beds, their effect tends to be, not to heighten, but to destroy 

 the red colour; while the more impervious strata are usually redder 

 than the more pervious. The American beds, according to the same 

 author, owe their colouration to the presence of ferric oxide which 

 was transported as such and deposited almost wholly as a mechanical 

 sediment, chiefly as a coating to sand-grains; but beyond saying that 

 the inauguration and cessation of red bed sedimentation was probably 

 connected closely with climatic and topographic changes involved in 

 the erogenic history of the continent no definite statement as to 

 climate is made. 



Case has also considered in detail the formation of the Permo- 

 Carboniferous Red Beds of Texas, and shows there is nothing in them 

 to oppose the most generally accepted hypothesis that the red colour 

 owes its presence to the mature weathering of iron-bearing rucks in 

 a fairly humid region, with alternations of relative drought and humi- 

 dity. The clays of Texas have a solidity and density which would 

 not be present if the colouration were due to oxidation and dehy- 

 dration of the iron subsequent to its deposition. 



Again, in his latest work (1919) lie says that flood-plain deposits 

 of arid regions are marked by the presence of highly oxidised or 

 carbonated minerals with a lack of hydrous oxides or sulphides. This 

 is largely due to the normally low water-table, which permits the 

 penetration of air deeply into the soil, and the exposure of the animal 

 constituents to oxidation or carbonation Also, the lack of vegetation 

 on an arid flat means a lack of carbon. The common result is the 

 prevalence of a red colour, the presence of gypsum associated with 

 the remains of terrestrial animals, and a lack of plant remains. 



There is thus a consensus of opinion with regard to the theory 

 that the iron oxide, which gives the red colour, is due to the de- 

 composition and oxidation of iron-bearing minerals and that it was 

 deposited in the red strata mechanically in its oxidised condition; but 

 its presence alone is not sufficient to make any pronouncement as to 

 whether the climate was humid or arid. If the red is not associated 

 with blue or grey or black, then the probability inclines towards the 

 arid climate or, more nearly, the semi-arid. 



