166 GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
to the Rio San Saba, Texas. Our survey has traversed this basis from the vicinity of Little 
Rock to Delaware mount, a distance of more than four hundred miles, coal being found almost 
everywhere from Petit Jean mountain to Coal creek and the Shawnee mountains. It forms a 
vast reservoir for the sustenance of industry and commerce along the whole line of the Pacific 
railroad. This carboniferous basin contains, in addition to the coal, an abundance of excellent 
sandstone for building bridges and embankments, good beds of limestone for the mannfacture 
of lime, and also iron. Artesian wells will give an immense supply of water for agricultural 
or other uses, and it may be predicted that this region will be one of the richest portions in the 
southern States of the Union. 
Immediately after crossing Delaware mount, which is formed of upheaved and dislocated beds 
of carboniferous limestone, whose direction is from south-southwest to north-northeast, we meet 
with horizontal beds of red and blue clay that belong to another geological epoch. This new 
formation, corresponding to that which European geologists have agreed to call the Trias, holds 
a very important position in the west; and it may be said, with some few exceptions—such as 
being sometimes covered by a more modern formation, or replaced by carboniferous, devonian, 
or modern rocks—with these exceptions, the Trias may be said to form the whole of the immense 
square comprised between the 96th and 114th degrees of longitude, and the 32d and 48th 
degrees of latitude ; extending one arm to the Sault St. Marie, at the entrance to Lake Superior, 
of which it forms a part of the contour. 
This formation, which I was the first to notice and recognise in the west, (a Geological Map 
of the United States and the British Provinces of North America, page 42,) attains a very con- 
siderable development, and, according to my observations, has a thickness of four or five thou- ` 
sand feet. The few observations as yet made on this American Trias, and its great extent of 
surface, prevent the establishment of very accurate divisions ; but, from what I have seen, I will 
establish provisionally three principal divisions in these Forks: 
The lower division is composed, especially at the base, of red and blue clay; the - predomi- 
nates as you ascend, and becomes of a vermilion color; then red sandstone, with green spots and 
a very friable texture, a massive and sometimes delfistdas stratification, VitoréálAtás with the 
clays, and finishes by entirely replacing them; this sandstone is very hiraat, like sand, 
though some beds are quite coarse, and Fébertiblo a sort of conglomerate. 
This lower group, which attains from two to three thousand feet of thickness, tritis o our whole 
route from Topofki creek to Rock Mary. I connect with this lower group the ved sandstone that 
forms more than half the contour of Lake Superior, as well as that which forms the shore of the ` 
Bay of Fundy, (Nova Scotia and New Brunswick ;) and also a part of the sandstone forming 
Prince Edward and the Magdalen islands. In Virginia and New Jersey, that part of the red 
sandstone which is without fossils and does not contain any gypsum, belongs to this lower 
division, which closely corresponds t» the bunten sandstein of the German geologists, the grès 
bigarés of the French, and to the upper New Red sandstone of the English. 
The second group, or middle division, is formed of beds of red clay, containing, very often, 
immense masses of white gypsum, Dee WEN furrowed with veins of crystallized gypsum, with 
interposition of strata of magnesian or dolomitic limestone, and frequently beds of rock-salt or 
saliferous clay are found superposed upon the gypsum. The height of the beds in this middle 
group is about fifteen hundred feet. We met with it on our route from Rock Mary to the arroyo 
Bonito, or Shady creek, with the exception of two points, where the direction taken by our expe- 
dition, near Camp No. 31, crossed strata of neocomien, and at Antelope Hills whitish-grey 
sti: which belongs to the upper division of the Trias. 1 connect with this middle group 
the gypsum found in the red sandstone of New Jersey; at Windsor, Nova Scotia; at Plaster 
cove, Cape Breton; and at Prince Edward island. As to its synchronism with European forma- 
tions, 1 regard it as corresponding to the muschelkalk of Germany. It contains, like the 
muschelkalk of Wurtemberg, rock-salt and dolomite. The first fossils which found in the 
Trias were in this division. It was near Camp No. 33—a full-grown tree, branches, very 
. 
