THE TRIASSIC PERIOD. 207 
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 colour, 
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 neighbouring 
shore. ‘The few fossils which may be considered as properly 
belonging to these deposits are chiefly Crustaceans (£stheria) 
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 Zavd, 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 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 Rhetic 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 Palzeo- 
zoic. In spite, therefore, of the great difficulty which is ex- 
perienced in effecting 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 Lefidodendroids, Asterophyliites, 
and Annularia, of the Coal and Permian formations, have now 
apparently wholly disappeared ; and the Triassic flora consists 
mainly of Ferns, Cycads, and Conifers, of which only the two 
