We may therefore conclude,
with considerable probability, that the barren sandy and marly
accumulations 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 highest members of the Trias are largely calcareous,
and are replete with the remains of undoubted marine animals. There
cannot, therefore, be the smallest doubt but that the Muschelkalk
and the Rhaetic or Koessen 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.
[Illustration: Fig. 140.--_Zamia spiralis_, a living Cycad.
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