444 MESOZOIC TIME REPTILIAN AGE. 



at the same time the Bengal beds contain Cycads, the coal has been referred by- 

 most authors to the Mesozoic, and either the Jurassic or Triassic period. 



In the Australian beds there are heterocercal Ganoids ,• and hence the forma- 

 tion cannot be more recent than the Triassic* Sixty miles south of Nagpur, at 

 Mangali, beds similar to those of Nagpur occur, which have been referred to the 

 same period, although there are no plants to demonstrate positive identity ; they 

 contain Estherias, homocercal Ganoids, and a species of LabyrintJwdont, — evi- 

 dently a Triassic assemblage of species. 



In view of all the facts, it appears probable that the coal beds referred to, both 

 in Asia and Australia, represent the Triassic period. 



There are other beds at Kota oh the Pranhita, related to those of Mangali. 

 There are still others at the Rajmahal Hills, in central India, the age of which 

 is more doubtful. They abound in Cycads, and fail of most of the genera 

 found at Nagpur : they have been regarded as Jurassic. 



JUEASSIC PERIOD (17). 



The Jurassic period derives its name from the Jura Mountains 

 on the western borders of Switzerland, one of the regions charac- 

 terized by the formation. 



1. AMERICAN. . 

 I. Rocks : kinds and distribution. 



On the Atlantic border, the upper portion of the formation 

 described in the preceding pages on the Triassic may belong, as 

 has been observed, to the Jurassic period. As no species of fossils 

 characteristic of any part of this period have yet been found in 

 the beds, there is some doubt on this point. The absence of Tri- 

 gonias, Belemnites, Ammonites, and other Jurassic forms, may, however, 

 be owing to the fact that the strata are not properly of sea-shore 

 origin. 



On the Gulf border there are no rocks of this period anywhere 

 exposed to view. 



* The author, iri his notes on Australian Geology, published in his Explor- 

 ing Expedition Geological Report (in which one of the Ganoids and many of 

 the coal plants are figured and described), referred the Australian beds to 

 the Permian period, on account of the presence of the heterocercal Ganoids, the 

 absence of Cycads, and the regular continuity of the beds with the Carboniferous 

 strata below. But the resemblance to the Indian flora must bring all to one 

 horizon, and the above conclusion seems best to harmonize the facts. Rev. W. 

 B. Clarke reports true Lepidodendra from the interior of New South Wales, — 

 from which it appears that the Carboniferous flora is represented on the Austra- 

 lian continent. 



