102 
IOWA ACADEMY OF SCIENCE Vor. XXIX, 1922 
Following the reports of the earlier Governmental Surveys the 
entire coal-bearing section was of the same age as the original 
Laramie beds. But the evidence brought forth demonstrated that 
while the section was, in its lower part, Cretaceous in age, in its 
upper part it was certainly of Tertiary age. The notable uncon- 
formity plane midway in the section demanded particular attention. 
More important than the determination of whether either part of 
the section was to be correlated with the typical Laramie of Wy- 
oming was the evaluation of the depositional equivalent of the un- 
conformity plane. 
In the Raton region the stratigraphic position of the great 
sandstone, known as the Trinidad sandstone, was readily deter- 
mined. This thick stratum manifestly rested directly upon the 
Pierre shales. The latter, called the La Jara shales on the farther 
side of the Rocky Mountains, were more than 1000 feet in thick- 
ness, and represented the uppermost member of the Coloradan 
series. The Trinidad sandstone, or the Pina Vititos sandstone as 
it is termed to the westward, and the 300 to 400 feet of coal- 
bearing shales beneath the plane of unconformity were all that 
were left of the enormously thick Montanan series. The erosion 
plane was an important one. 
Since, as indicated by abundant plant remains, the upper 1500 
feet of the section was Early Tertiary in age, it was quite evident 
that the unconformity plane represented a very long interval of 
time. Fully one-half of the great Cretaceous succession was miss- 
ing. 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 4000 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 2 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 
erosion in this. 
2 U. S. Geol. Surv., Prof. Pap. No. 101, p. 56, 1917. 
