EESUME 
OF A 
GEOLOGICAL RECONNAISSANCE, 
EXTENDING 
FROM NAPOLEON, AT THE JUNCTION OF THE ARKANSAS WITH THE MISSISSIPPI, TO THE 
PUEBLO DE LOS ANGELES, IN CALIFORNIA. 1 
BY JULES MARCOU, GEOLOGIST AND MINING ENGINEER. 
Boston, July 26, 1854. 
Dear Sir : In obedience to tlie instructions contained in your letter of the 2d July, dated 
Washington city, D. C., I have the honor to send you the Resume of the geological reconnais¬ 
sance that I made in connexion with your survey for the southern Pacific railroad, extending 
from Napoleon, on the Mississippi, to the Pueblo de los Angeles, in California. 
Having in my possession, as yet, neither the specimens which I collected, nor a good map of 
the country passed through, and the time being very short which is left me to make my report, 
I trust you will excuse the brevity of this Resume ; in which, however, I will endeavor to show 
the principal geological results of my exploration, in order to give a general idea of the mine- 
ralogical resources of the route with regard to the construction of a railroad. 
Napoleon is situated on the alluvium of the Mississippi; which extends on the two hanks of 
the river Arkansas as far as Little Rock, and is composed of a very fine-grained, reddish-yellow 
earth. This alluvial deposite forms the richest agricultural portion of the State of Arkansas; 
and as it constitutes the whole of the basin which extends from Little Rock to the Mississippi, 
and is always in horizontal beds, these rocks, it will he seen, offer no obstacle to the construc¬ 
tion of a railroad. 
At Little Rock the alluvium is replaced by rocks, forming a line of mountains, whose direc¬ 
tion is from west west-south to east east-north. 
These rocks continue for three or four miles along the river, and are formed of black slates, 
of grey, quartzose metamorphic masses, traversed by veins of white quartz, having the same 
direction as the mountains. 
On the left bank of the Arkansas, two miles higher than Little Rock, the sandstones and lime¬ 
stones of the carboniferous period begin to appear, resting horizontally upon the metamorphic 
rocks. Here begins the fine coal-basin of Arkansas, which is only a continuation of the immense 
coal-field of Iowa, Missouri, Kansas, and which extends even to Fort Belknap, Rio Brazos, and 
1 This Resumd is reprinted from the preliminary or first report of Lieutenant Whipple, in 8vo., Chap. VI, p. 40 
(Reports of Pacific Railroad Surveys, House Doc. 129 : Washington, 1855.) 
