CHAPTER ITI. 
OBSERVATIONS ON THE GEOLOGY OF THE ROUTE. 
SANTA FE, ALBUQUERQUE, AND THE VALLEY OF THE RIO GRANDE DEL 
NORTE. 
GENERAL REMARKS.—SANDIA AND SANTA FÉ MOUNTAINS.— VIEW OF ALBUQUERQUE AND THE SANDIA MOUNTAINS. —CARBONIFEROUS 
LIMESTONE.— GRANITE.— FOSSILS.— RELATIVE POSITIONS OF THE STRATA.—COAL MEASURES.—ABSENCE OF OUTCROPS ON THE WEST 
SIDE OF THE MOUNTAINS. —METAMORPHIC ROCK.-—GRANITE.—TRAP-DYKES.— AT GALISTEO AND THE HEAD-WATERS OF THE TUERTO.—- 
RESEMBLANCE TO RUINS AND WALLS.— QUARTZ VEINS.— VOLCANOES AND LAVA, CERRITOS.— PLAINS OF LAVA OR BASALT.— DLUFF AT 
SAN FELIPE.—SEDIMENTARY DEPOSITES OF THE VALLEY OF THE RIO GRANDE.—BLUFFS AND HORIZONTAL BEDS.— 
THE STRATA TO THOSE ON THE CANADIAN.—CRETACEOUS FOSSILS AT POBLAZON.—SANDSTONE AND SELENITE.— PROBABLE CRETACEOUS 
AGE OF THE STRATA IN THE VALLEY OF THE RIO GRANDE.—-ALLUVIAL DEPOSITES.—SOIL OF THE VALLEY OP THE RIO GRANDE.—- 
SAND-DUNES.— VALLEY OF THE PUERCO. 
Although the line of survey did not extend north as far as Santa Fé, this place was visited 
by Mr. Marcou, and notes were made upon the geology. Some of the most interesting fossils of 
the collection are from this vicinity—from the Pecos villages at the southern end of the Santa 
Fé mountains. The geology of this part of the route becomes much more intricate and inter- 
esting, as, instead of horizontal strata exposed at most to the depth of a thousand feet, we have 
the varieties of the intrusive rocks traversed by mineral veins, and flanked by uplifted strata of 
different ages and lithological characters. 
A general description of the wide valley between the two principal ranges of mountains—the 
Santa Fé and Sandia on one side, and the Sierra Madre on the other—has already been given, 
(see Chapter I,) and the fact that the Rio Grande occupies a small part of the space, and that its 
channel is confined to the eastern side of the valley, has been shown. The settlements in that 
region being chiefly upon this river, are confined to the vicinity of the eastern ranges, the Sandia 
and Santa Fé, and the geological observations, are, therefore, more numerous and complete 
around them than on the western side or among the ridges of the Sierra Madre. As the pre- 
ceding descriptions have extended along the route up to the base of the first mentioned ranges, 
their geological structure will be first considered. 
Sandia and Santa Fé mountains.—Previous to the exploration of Lieutenant Whipple, we 
were aware that the main axis of these mountains was granitic, and that stratified limestones were 
found in them; but of the age of these strata, and of their relative position to the granite, there 
appears to have been but little or no reliable evidence. Mr. Marcou's notes, however, and the 
collection of fossils from the eastern base of the range, leave us no longer in doubt on these 
points 
These mountains present almost vertical escarpments towards the west, and when seen from 
Albuquerque or its vicinity, the sky outline appears very regular and straight and is suggestive 
of the edges of stratified rocks. The annexed sketch was taken by Mr. Campbell, from the 
Camp beyond Albuquerque, and the peculiar form of the summit of the mountains is distinctly 
shown. 
The examination of the mountains verifies the indications, and we find granite and the 
associate rocks at the base, and at the summit thick strata of carboniferous limestone dipping 
eastwardly at angles of 25 or 30 degrees, and so passing under the strata of the Llano which have 
been described. These limestone strata are associated with shales, which are black, and from 
