LARAMIAN HIATUS AROUND THE SOUTHERN 
ROCKIES 
CHARLES KEYES 
For a long time after the vast coal fields which extend around 
the southern extremity of the Rocky Mountains in southern Colora- 
do and northern New Mexico, came under close surveillance of 
stratigrapher their deposition was regarded as having taken place 
during the closing epoch of the Cretacic Period. The great thick- 
ness of the associated strata were paralleled with the enormously 
thick Laramie coal-bearing beds of Wyoming and Montana. On 
this point a voluminous literature appeared to be in general agree- 
ment. 
When, in 1902, it was my privilege first to enter the New Mex- 
can coal-fields under the aegis of Railroads then building, I soon 
began to suspect and then to entertain doubts as to the correctness 
of the reference of the entire great rock section to the Laramie 
coal series. Casual examination of fossils collected and identified 
indicated that the principal coal-yielding strata were really well 
down in the Cretaceous column. A considerable part of the upper 
portion of the vertical section was in like manner determined to be 
certainly very much younger. At the coal camp of Hagan, to 
the westward, at the eastern base of the Sandia Range, the Cretacic 
rocks were displayed in full detail. Above the top of a published 
section 1 the beds were made out to be Tertiary in age. They en- 
closed 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 spe- 
cial 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 Tertiary beds was soon 
divined. An erosional unconformity was found to bej 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. 
l Eng. and Mining Jour., Vol. EXXVII, p. 670, 1904. 
