MESOZOIC ERA: THE AGE OF REPTILES 569 



REFERENCES FOR PLANTS 



Chamberlin and Salisbury, — Geology, Vol. 3. 



Knowlton, F. H., — The Relations of Paleobotany to Geology: Am. Naturalist, Vol. 46, 



1912, pp. 207-215. 

 Seward, A. C, — Fossil Plants. 

 Scott, D. H., — Studies in Fossil Botany. 

 Scott, D. H., — Evolution of Plants. 



Scott, D. H., — Paleobotany: Encyclopedia Brittanica, nth edition. 

 Scott, W. B., — An Introduction to Geology, pp. 668, 684, 714-715. 

 Stopes, M. C, — Ancient Plants. 

 Wieland, G. R., — American Fossil Cycads. 



Climate 



Triassic. — The climate of the Triassic of North America, Central 

 Europe, and North Africa seems, as a whole, to have been arid, al- 

 though some areas of considerable extent had sufficient rainfall to 

 produce a luxuriant vegetation. The proofs of aridity are to be found 

 in the widespread occurrence of gypsum and salt, and in the preva- 

 lence of " red beds " (rock of a red color). It is well known that the 

 deposition of salt and gypsum is the result of evaporation in excess of 

 supply, such as can happen only in arid regions. The explanation 

 of the red color of sedimentary rocks is not so clear. If organic matter, 

 either animal or plant, is plentiful in sediments, the contained iron 

 will be in the form of the gray iron carbonate instead of the red iron 

 oxide. At the present day, for example, although the rocks of the 

 southern Appalachians are weathered to red clay many feet deep, 

 the sediments derived from them are gray when deposited, because of 

 the reduction of the iron oxide by the plant debris which they inclose. 

 A less abundant flora, due to decreased rainfall, might readily result 

 in the deposit of red sediments without reduction. On the other hand, 

 attention has been called to the fact that, probably in many cases, 

 red sediments were laid down in regions where the rainfall was un- 

 doubtedly not small. (White.) 



The Triassic red sandstones and shales of the Connecticut valley, 

 with their innumerable reptilian footprints, indicate aridity in another 

 way. It was formerly thought that these deposits were laid down in a 

 great estuary of the sea, under conditions similar to those of the Bay 

 of Fundy to-day, in which the difference between high and low tide 

 was great. As a result, during several hours of the day, extensive 

 mud flats were uncovered, upon which the saurians of that time walked 



