_Sedimentary Formations._ During the epochs of greatest overflow great
marine formations were deposited over large areas of what is now dry
land. These were followed as the land rose to sea level by extensive
marsh and delta formations, and these in turn by scattered and
fragmentary dry land deposits spread by rivers over their flood
plains. In the marine formations are found the fossil remains of the
sea-animals of the period; in the coast and delta formations are the
remains of those which inhabited the marshes and forests of the coast
regions; while the animals of the dryland, of plains and upland, left
their remains in the river-plain formations.
[Illustration: Fig. 5.--Geologic Cycles and the Land Area of North
America (after Schuchert).]
These last, however, fragmentary and loose and overlying the rest,
were the first to be swept away by erosion during the periods of
elevation; and of such formations in the Age of Reptiles very little,
if anything, seems to have been preserved to our day. Consequently we
know very little about the upland animals of those times, if as seems
very probable, they were more or less different from the animals of
the coast-forests and swamps. The river-plain deposits of the Age of
Mammals on the other hand, are still quite extensive, especially those
of its later epochs, and afford a fairly complete record in some parts
of the continent of the upland fauna of those regions.
_Occurrence of Dinosaur Bones.
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