OF NORTH AMERICA. 
25 
In the Cajon Pass 1 found granite, sienite, trap and serpentine, exactly similar to those found 
between Rough and Ready, Grass valley and Nevada City, and which contain the veins of auri- 
ferous quartz. 
As specimens were given to me at Los Angeles, very rich in gold, coming from the Cajon 
Pass, it is more than probable that this point will, one day, be one of the richest Placeres in California. 
In an economical point of view, the eruptive rocks which form almost the whole country be- 
tween Cactus Pass and Cajon Pass will furnisb excellent materials for construction, for bridges, 
roads, and bouses; there are also very beautiful marbles, red porphyry, and especially, I think, 
will be found there, mines rich in silver and gold. 
Before concluding, I will say that the relative age of the Sierra Nevada is much less than 
that of the Rocky Mountains, although the direction of the two chains is the same — that of the 
meridian. The Coast Range was raised at the end of the Eocene epoch, whose beds it has up- 
heaved and dislocated, as may be seen in the environs of Monterey; and the Sierra Nevada was 
raised later, at the end of the Miocene, or Pliocene; I have not been able to determine to which 
of these two this System of dislocation corresponds. 
Accompanying this will be found a Geological Section ') of the country passed through , as 
correct as possible, for the short time I have left to make it. 
I am, dear sir, your most obedient servant, 
JULES MARCOU, 
Geologist and Mining Engineer of the Expedition. . 
A. W. Whipple, first Lieut. Top. Eng., V. S. A.. 
In. charge of Exploration of route near 35*'' parallel. 
*) The geological profde accompanying this report: see frontispiece, is not a speculative one ; I have traversed 
every inch of ground comprised in it, and if it does not mathematically represent all the features of the country 
on the line from Fort Smith to the Pueblo de los .\ngeles. it is owing to the smallness of the scale. 
The heights are exaggerated in relation to the distances, though they are by no means absurdly dis- 
proportioned. I adopted this profile after numerous trials, and I must say that it apficars to me to give 
the same general asjject that presents itself to the eye of the observer from the summits of the Rocky 
Mountains, the Sierra do San Francisco and the Sierra Nevada. I know there is a great difference be- 
tween this appearance and a true profile , where the proportions of the heights and distances are the 
same, and where the curve of the earth’s surface is considered. But I thought it more useful to give 
an idea of that which strikes the eyes of travellers in those regions, than to establish an exact and ri- 
gorous trigonometrical profile. 
The distances and the heights are copied from the profile made bv Lieut. Whipple , the Commander 
of our expedition. 
This Geological Section may be regarded as the resume of my Report and of what I saw' in my ex- 
ploration. I have taken the greatest care in gicing the superpo.sition of the rocks , their concordant and dis- 
cordant stratification , and there is nothing supposed or doubtful, it is the result without exception of direct 
and numerous observations. To understand this section perfectly, not only must the Report to Lieut. 
Whipple be consulted, but the Geological Map beneath it, must be attentively regarded. The position 
in which the Secretary of War, Jefferson Davis, has placed me, and the delivery of my note-books to 
a mineralogist with whom I have no acquaintance and who has further shown himself to be unfriendly, 
obliges me to define my observations precisely, in order to leave the least opportunity possible for 
hostile criticism, which seeks to make me say what I have never said, and even the contrary of what 
1 have written and printed in two or three languages. 
..■a-. 
