58 : GEOLOGY. 
The granite forming the base of the series is very compact and massive, scarcely showing 
any tendency to stratification. It is cut by veins of quartz of large size, and contains veins and 
masses of handsome red syenite and coarse red felspathic granite, with plates of silvery mica. 
All these seem to have been injected into fissures. 
The erosion of the cafion has beautifully displayed the ancient surface of the granite, and 
shows it to have been extremely irregular; hills several hundred feet high, many of which have 
precipitous sides, and deserve the name of pinnacles, have been exhumed from the sediments 
in which they were enveloped. The sandstones and shales are seen to have been deposited 
quietly around them; their strata, nearly horizontal, abutting against their sides. We have 
here evidence that at least these granite hills are older than any of the stratified rocks of the 
table-lands.—(See preceding page.) 
Retracing our steps, as the only means of exit from the bottom of the Colorado cafion, and 
reaching the surface of the mesa, a short distance east of Camp 66, we obtained a fine panora- 
mic view of the geological structure of the country for many miles about us. 
We stood upon the gray cherty limestone which caps the cliffs on the Colorado, and which 
forms the surface rock over a large area. It here contains large quantities of iron in nodules, 
with few fossils, except masses of coral. Below us, on the west, was the broad eroded valley 
or plain, across which we had approached the Colorado. On the east the bold escarpments of 
a higher mesa limited our vision in that direction and formed a series of headlands, which 
diminished in perspective toward the north and south. 
From this point the view towards the north was particularly grand; the course of the Colorado 
was visible for nearly a hundred miles, and the series of Cyclopean walls into which the mesas 
of different elevations have been cut by that stream and its tributaries formed a scene of which 
the sublime features deeply impressed each member of our party. Some conception of the 
character of this scenery may be gathered from the sketches of the artists of the party, Messrs. 
Egloffstein and Mollhausen. 
As we progressed towards the east we found the surface of the Mountain limestone consider- 
ably eroded, and in places covered with heavy beds of alluvial gravel; the nodules of chert, 
which it contains in such abundance, having been left in its decomposition, cover the surface, 
and with their many angles seriously incommoded our mules. 
Approaching the high mesa we ascended rapidly, and for the first time since leaving the 
Pacific were surrounded by arborescent vegetation sufficient to deserve the name of forest. 
There is here apparently a local interruption of the general easterly dip which I have said 
prevails over all the western portion of the table-lands, and a slight arching of the strata over 
what seems to be the continuation of the line of upheaval marked further south by the Picacho 
and other mountains of like character in that vicinity. At one point between our Camps 68 and 69 
the stratified rocks have been broken through by the eruptive force and a mass of trap has 
been protruded. The quantity of erupted material is however small, and, as in many similar 
cases which came under our notice, it has produced little or no dislocation of the sedimentary 
strata. 
HIGH MESA WEST OF LITTLE COLORADO. 
East of that portion of the table-lands which I have described is a belt of country from thirty 
to fifty miles in width, extending from a point south of the San Francisco mountain north- 
westerly into Utah, which has a much greater elevation than that on either side of it, and forms 
a natural water-shed between the tributaries of the Colorado, flowing in a northwesterly direction. 
Where we crossed this divide it has the character of an elevated plateau, of which the surface 
has been considerably modified by erosion, and now presents many broad and shallow excavated 
valleys. Its geological substrata are everywhere middle or upper Carboniferous rocks, which, 
though exhibiting local variations from the general eastern dip, nowhere show any disruption 
or contortion. 
