Summary of Conclusions Reached 509 



freshwaters. The striking Permian deposits of France, 

 of Bohemia, and of Texas with their floral and faunal 

 features are specially referred to. 



Chapter 6. The physical and biological environment of 

 fishes during Triassic-Jurassic time. 



The Triassic formation reveals frequent and at times 

 alternating deposits of freshwater and marine character, 

 some of which are treated of. In the marine deposits 

 fishes, amphibians, land plants and other ecologically re- 

 lated organisms are absent. In the freshwater deposits 

 a varied and abundant fish-life is revealed. But the ganoid 

 fishes are now predominant, while the elasmobranch and 

 to some degree the dipnoan types are rarer. 



Comparison is made of the British, Austrian, Italian 

 and Eastern States fauna. While the last has been regarded 

 by Newberry and successors as freshwater in origin, they 

 and European palaeontologists have viewed the others 

 as marine. The writer shows that all were closely similar 

 in origin and were freshwater organisms. The rich fish- 

 beds and the associated petroliferous products are corre- 

 lated with extensive and active volcanic and diastrophic 

 changes. The wide development of the system from Texas 

 down to extreme southern parts of South America indicates 

 far reaching continental deposits. 



The nature of the beds, and the organisms — especially 

 the fishes — that make up the Karoo series of S. Africa, 

 the Triassic of India, and the Gosford-Hawkesbury beds 

 of Australia are considered, and comparison is made of the 

 types of fish — mainly freshwater ganoids — that occur in 

 these. 



The Jurassic system is of interest as showing in its 

 upper beds proof of a commencing remigration of Elasmo- 

 branchs, and also a primary migration of gano-teleostean 

 fishes into a marine environment. This result was a sum- 

 mated biologic reaction to frequent sea encroachments, to 

 reduction in some regions of lake and flood-plain areas, to 

 aggressive action of increasingly larger land and freshwater 

 reptiles, to increasing perfection in defensive and even more 



