CHAPTER VI. 
GENERAL DESCRIPTION OF THE GEOLOGICAL FORMATIONS. 
GRANITIC, METAMORPHIC, DEVONIAN, AND CARBONIFEROUS. 
General remarks.—Granitic and metamorphic rocks predominate west of the aztec mountains.-—Red or pink granite 
PREDOMINATES.-PRINCIPAL PLACES AT WHICH METAMORPHIC ROCKS HAVE BEEN IDENTIFIED.—THEIR PROBABLE AGE.-AZOIC.- 
Silurian.—Carboniferous.—Relative ages of the granitic chains.-—Anterior to and later than the carboniferous.— 
Tertiary or post tertiary.—Ranges of the same age not coincident in direction.—Devonian, uncertainty of its 
existence.—Carboniferous.—Of tiie sandia and santa fe mountains.—General extent along the line.—Lithological 
characters.—Thickness of the strata.—Fossils.—Sandstone and coal measures.—Lithological characters.—View near 
fort coffee.—Overhanging strata at sugar-loaf mountain.—Ferruginous sandstone,.—Thickness of the coal measures.— 
Diminish towards the west.—Fossils.—Coal.—General observations on the carboniferous formation.—Disturbances of 
THE FORMATION.-DENUDATION.—LIMESTONE OF CANON DIABLO.-METAMORPHIC LIMESTONE OF THE CAJON AND TEJON, PROBABLY 
CARBONIFEROUS. 
GRANITIC AND METAMORPHIC. 
In. a rapid reconnoissance of any region in a direct line, it is impossible to bestow that atten¬ 
tion upon the phenomena presented by the disturbed and metamorphosed rocks which their 
obscured condition demands. The mineral characters and relations of unchanged horizontal 
strata are ever present to the view along the valleys and ravines ; but the folded and crumpled 
remnants of older strata can only be seen at intervals, and present an endless variety of condi¬ 
tions and appearances, serving to confuse and perplex even the observer who has time at his 
command. It is not, therefore, possible to assign the dividing lines between the truly erupted 
granitic rocks and those which simulate them, but are in reality of sedimentary origin. We 
can only state that here and there the metamorphosed stata are found, but their connexion can¬ 
not yet be shown. Neither can the granitic rocks be separated into their several varieties, nor 
the different intrusions be shown. It is therefore necessary to group all these rocks under one 
head as above, and to represent them by one tint on the map. The presence of metamorphic 
strata has, however, been indicated at several points on the section. 
The rocks of this group predominate on the western portion of the line. The region where 
the mountains are most numerous and abrupt is also, as is usual, the region of the greatest 
granitic exposure. West of the Aztec mountains nothing but these rocks and the more modern 
sedimentary formations are visible. On the central and eastern portions of the line, and indeed 
for nearly four-fifths of its entire length, but few exposures of the granitic and metamorphic rocks 
are found. The area of these outcrops is also comparatively limited. The granite foundations 
over this broad area, from the Mississippi to longitude 112°, are nearly covered from view by thick 
strata of Palaeozoic and Secondary age. The outcrops of granite are found only in narrow lines, 
peering here and there above the broad and level plateau. The principal lines, however, con¬ 
stitute the great crest or water-shed between the two oceans. They are the most elevated portions 
of the country, and consist of the Sierra Madre, Santa Fe mountains, and Sandia mountains. A 
subordinate line, and one with an entirely different direction, is found in the Witchita mount¬ 
ains and the outcrops between them and Little Rock. These lines of elevation are the only 
exposures of granitic rock found on the line between the Mississippi and the volcano of San 
Francisco. 
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