8o The American Geologist. February, 1903. 
west. In the canyon of the Pnerco river, about five miles south 
of Cabizon, 800 feet of strata are exposed in vertical section. 
The rocks of this exposure are orange colored sandstones and 
dark fissile shales, except the lower 150 feet which are gypsi- 
ferous in structure and probably Jurassic in age. 
The Fort Union Beds. — The group of rocks here designat- 
ed as Fort Union lie conformably on the Fox Hills. They are 
found both to the north and also to the south of the eastern 
extension of the Fox Hills. They are known as the coal group, 
and are 500 feet in thickness. They show a predominance of 
soft yellow sandstone, interbedded with clays and sandy shales. 
They contain strata of brown coal which are freely exposed in 
perpendicular walls of the mesas. The coal seams in the Jemez 
coal fields south of Mesa Blanco, near San Isidro, are from 
two to twelve feet in thickness ; and along one fault in this 
coal area, seventy feet of coal are exposed in one view. In 
examining these coal fields it was observed that in many in- 
stances the strata had been destroyed by lire ; and, the coal be- 
ing burned out, the roofs had caved in by a succession of fault- 
ing or had collapsed under pressure. That the destroying 
agent was fire is attested not only by the clay accompanying 
the «eams being transformed into brick, but also by masses of 
slag composed of the silicates of iron and aluminum. This 
coal is bituminous and is Fort Union or Laramie. It is very 
brittle, somewhat laminated, and of dull luster. 
In speaking of the coal outcrop near Nacimiento, Mr. 
Loew in the U. S. Geographic Surveys of the Territories, says : 
"The strata of brown coal are freely exposed in the per- 
I)endicular walls of the mesas, and are accompanied by shales, 
slate, clay and sandstone. Their thickness varies from six 
inches to eight feet. In some instances the strata have been 
])artly destroyed and undoubtedly by fire, as evidenced not only 
of the accompanying clay being burned to brick but also by 
heaps of slag composed of silicates of iron and aluminum. . .It 
is bituminous and Cretaceous, not coking; very brittle, some- 
what laminated, luster dull."^ 
Flad this same writer visited the coal fields southwest of 
San Isidro to the south of Mesa Blanco, he could have de- 
scribed them with exactly the same words that he has used in 
describing the coal outcrop at Nacimiento. The coal is iden- 
tical, is Cretaceous and Fort Union or Leramie. 
