STRATIGRAPHICAL GEOLOGY 
151 
displayed in full detail. Above the top of the published section ^ 
the beds were made out to be Tertic in age. They enclosed a fine 
petrified forest. 
When, a little later in the season, with this clue to work from, 
the Raton and Trinidad coal-fields were made the subject of 
special investigation for the direct purpose of narrowing the limits 
of new prospecting as much as possible, the horizon separating 
the Cretacic strata from the supposed Tertic beds was soon di¬ 
vined. An erosional unconformity was found to be well-marked 
by a thick, local conglomerate, but the level proved to be in some 
localities much lower in the section than was anticipated. In 
places the basal conglomerate reached so low as the Trinidad 
sandstone, a notable guide-horizon just above the top of the 
Pierre shales. 
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, Cretacic in age, in 
its upper part it was certainly of Tertic age. The notable uncon¬ 
formity plane midway in the section demanded particular atten¬ 
tion. More important than the determination of whether either 
part of the section was to be correlated with the typical Laramie 
of Wyoming, was the evaluation of the depositional equivalent of 
the unconformity plane. 
In the Raton region the stratigraphic position of the great sand¬ 
stone, known as the Trinidad sandstone, was readily determined. 
This thick stratum manifestly rested directly upon the Pierre 
shales, was called in part the La Jara shales on the farther side 
of the Rocky Mountains, was more than 1,000 feet in thickness, 
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 1,500 
feet of the section was Early Tertic in age, it was quite evident 
that the unconformity plane represented a very long interval of 
1 Eng. and Mining Jour., Vol. EXXVII, p. 670, 1904. 
