THE MISSISSIPPIAN PERIOD 619 



main. There are reasons for thinking that amphibians frequented 

 the fresh waters and the adjacent lands, but probably not the seas. 



II. The Land Life of the Mississippian 



Since the period was one of sea extension and its known deposits 

 mainly marine, the record of land life is poor. There was doubtless 

 some notable restriction of the terrestrial life by reason of the en- 

 croachment of the sea. Enough fossil vegetation has been recovered 

 to show that the plant life of the early Mississippian land was 

 little more than an expansion of that of the preceding period. 

 There were, however, notable changes in detail. The geographic 

 diversity of the Mississippian floras was somewhat greater than that 

 of the Devonian floras. The mid-Mississippian flora is thought 

 by White 1 to have had its origin on the islands of western Europe, 

 and to have spread thence to Siberia and southward, even to South 

 Africa and Australia; but by what route is not known with cer- 

 tainty. Seventy-five per cent of the species of a Mississippian 

 flora of Argentina are identical with European species, a fact 

 which suggests strongly a land bridge between South America 

 and the continents just named. 



The floras of the early and middle parts of the period are better 

 known than those of its closing stages. The flora of the latter 

 indicates adverse conditions of life, and prepares the way for the 

 great floral changes, largely exterminative, which followed. From 

 this stage comes the only American pre-Permian wood (Dadoxy- 

 lon pennsylvanicum) which shows rings. 



The most interesting suggestion of advance in land life is found 

 in the footprints of a supposed amphibian (Peleosauropus [Sauropus] 

 primcevus) from the Mauch Chunk shale near Pottsville, Penn. 

 They imply a stride of about thirteen inches, and a breadth between 

 outer toes of eight inches. Nearly complete specimens of amphibia 

 (labyrinthodonts) have been found in the Lower Carboniferous of 

 Scotland. 



Probably the insects and their allies found in the preceding 

 system were represented, but their fossils are not known to have 

 been found. 



1 Jour, of Geol., Vol. XVII, 1909. 



