LARAMIAN HIATUS 
103 
There is, however, a larger aspect of the Laramian uncon- 
formity plane which should be noted. It is a critical expression 
of that great sedimental revolution which closed the Mesozoic 
era on this continent. The grand effects of this crustal movement 
were apparently not alone epeirogenic in their nature, but they 
were locally orogenic also. New Rocky Mountains came into ex- 
istence; although at a still subsequent date the area thus elevated 
was again leveled to the level of the sea. When sedimentation 
was renewed in the region it was Tertiary deposition, perhaps 
earlier than any Eocene deposit that we know elsewhere. 
The old Laramian planation surface is one of wide extent. It 
is also well displayed on the west side of the present Rocky 
Mountains uplift, in the High Plateaus of eastern Utah. In 
magnitude and importance it seems in every way comparable to 
the vast Comanchan peneplain, since it extended over all the south- 
ern Rocky Mountain tract. It appears to match the great Miocene 
peneplanation which the same region afterwards suffered. Its 
record forms one of the most prolix chapters in Rocky Mountain 
history. 
The Laramian hiatus recalls to mind our own Arkansan hiatus 
at the base of our Iowa Coal Measures. Like our Iowa interval 
enormously thick deposits are represented elsewhere. Perhaps 
our own Coal Measures gave clue to the solution of the Laramian 
problem which for more than half a century so completely baffled 
all mining men and geologists. Laramian events are manifestly 
very much more important than has been commonly, supposed. 
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