212 HISTORICAL PALEONTOLOGY. 



notice a difference as concerns the different members of the 

 group similar to that which has been already mentioned in 

 connection with the Permian formation. The arenaceous 

 deposits of the series, namely, resemble those of the Permian, 

 not only in being commonly red or variegated in their color, 

 but also in their conspicuous paucity of organic remains. 

 They for the most part are either wholly unfossiliferous, or 

 they contain the remains of plants or the bones of reptiles, 

 such as may easily have been drifted from some neighboring 

 shore. The few fossils which may be considered as properly 

 belonging to these deposits are chiefly Crustaceans (Estheria) 

 or Fishes, which may well have lived in the waters of estuaries 

 or vast inland seas. We may therefore conclude, with con- 

 siderable probability, that the barren sandy and marly accumu- 

 lations of the Bunter Sandstein and Lower Keuper were not 

 laid down in an open sea, but are probably brackish-water 

 deposits, formed in estuaries or land-locked bodies of salt 

 water. This at any rate would appear to be the case as regards 

 these members of the series as developed in Britain and in 

 their typical areas on the continent of Europe ; and the origin 

 of most of the North American Trias would appear to be 

 much the same. Whether this view be correct or not, it is 

 certain that the beds in question were laid down in shallow 

 water, and in the immediate vicinity of land, as shown by the 

 numerous drifted plants which they contain and the common 

 occurrence in them of the footprints of air-breathing animals 

 (Birds, Reptiles, and Amphibians). On the other hand, the 

 middle and the highest members of the Trias are largely calca- 

 reous, and are replete with the remains of undoubted marine 

 animals. There cannot, therefore, be the smallest doubt but 

 that the Muschelkalk and the Rhsetic or Kossen beds were 

 slowly accumulated in an open sea, of at least a moderate 

 depth; and they have preserved for us a very considerable 

 selection from the marine fauna of the Triassic period. 



The plants of the Trias are, on the whole, as distinctively 

 Mesozoic in their aspect as those of the Permian are Palaeo- 

 zoic. T n spite, therefore, of the great difficulty which is ex- 

 perienced in e-ffecting a satisfactory stratigraphical separation 

 between the Permian and the Trias, we have in this fact a 

 proof that the two formations were divided by an interval of 

 time sufficient to allow of enormous changes in the terrestrial 

 vegetation of the world. The Lepidodendroids, Aster ophyllites, 

 and Annularies, of the Coal and Permian formations, have now 



