152 
STRATIGRAPHICAL GEOLOGY 
time. Fully one-half of the great Cretacic succession was missing. 
If it ever existed in the region, and it doubtless did, it had been 
entirely removed by erosion. If ever any Laramie beds were 
present they, too, in like manner, had been swept away. 
Out of the 4,000 feet of vertical section once believed to repre¬ 
sent the Laramie formation not a single foot could now be so 
regarded. The vast Laramie pile of sediments elsewhere clearly 
had no depositional representation here. Stratigraphically the 
Laramian horizon was merely the horizon of the unconformity 
plane. But the latter possibly represented a time interval even 
longer than that in which typical Laramian sediments were laid 
down. Lately W. T. Lee ^ came to the same conclusion. In the 
Raton region the tremendously thick Laramie section elsewhere 
was represented by a complete void. It was a Laramie hiatus. 
Deposition took place in other parts of the country; subaerial in 
this. 
There is, however, a larger aspect of the Laramian unconform¬ 
ity 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 was ap¬ 
parently not alone epeirogenic in their nature, but they were locally 
orogenic also. New Rocky Mountains came into existence; al¬ 
though at a still subsequent date the area thus elevated was again 
planed off to the level of the sea. When sedimentation was re¬ 
newed in the region it was Tertic 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 Moun¬ 
tains uplift, in the High Plateaus of eastern Utah. In magnitude 
and importance it seems in every way comparable to the vast Co- 
manchan peneplain, since it extended over all the southern Rocky 
Mountain tract. It appears to match the great Miocene peneplan- 
ation 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 the Arkansan hiatus at the 
base of the Iowa and Missouri Coal Measures. Like in the case 
of the Iowa interval enormously thick deposits are represented 
elsewhere. Perhaps Iowa Coal Measures gave clue to the solu- 
2 U. S. Geol. Surv., Prof. Pap., No. 101, p. 56, 1917. 
