62 
GEOLOGY 
The environs of Cincinnati, Ohio; Madison, Indiana; and Frankfort, Kentucky; present a fine 
development of the Silurian, entirely distinct from the band above mentioned. It is the same with 
the Silurian of the vicinity of Nashville, these rocks occupying the middle part of the State of Ten- 
nessee. The Silurian is found on the Lower Missouri from the environs of S‘ Louis to Jefferson 
and Franklin’, and forms part of the mountains situated in the south-eastern part of the State of Missouri. 
Finally, Roemer has met with Silurian strata in Texas, where they form two narrow bands near 
the Rio San Saha and the Rio Llano. I found no trace of the Silurian in the Rocky mountains or 
the Pacific region, and I doubt if it exists there. 
Devonian formation. — Although the Devonian formation holds an important place among the 
American rocks, it has not so great a stratigraphical and geographical development as the Silurian. 
It attains its maximum of importance in the States of New York and Pennsylvania, where, as in 
Europe, it is divided into two principal groups. The Lower group is chielly formed by strata of 
limestone and clay, and the Upper by beds of red sandstone. A part of the strata at Schoharie near 
Albany, and the whole of the Ilelderberg mountains belong to the Lower group, w'hile the Upper 
group forms the Catskill mountains. In the other parts of North America where the Devonian 
is found, it consists of a group of limestone strata containing numerous fossils, and the falls of the 
Ohio near Louisville , and the island of Mackinaw' in Lake Huron , may be taken as types of this for- 
mation. The fossils characterizing the Devonian are: species belonging to the genus Calymene, Te- 
rehralula , Spirifer , Chonetes , Zaphrentis , Emmon.na , and Syringopora. 
On looking at the Geological Map see frontispiece — we shall see that the Devonian recog- 
nized near Gaspe, Lower Canada, occupies a part of that peninsula and enters the north-western 
part of New' Brunswick. Beginning in the south-eastern part of Tennessee it follows up the whole 
line of Alleghany mountains, covers entirely the southern part of the State of New York, and em- 
braces the w'hole of Lake Erie and Lake S' Clair , and a part of the shores of Lake Huron and 
Lake Michigan. It descends from Lake Erie to the Ohio valley and surrounds the Silurian of Cin- 
cinnati and Frankfort, then reaches the northern part of Illinois, crosses the Mississippi near Da- 
venport, and runs up the valley of the Red Cedar river in the State of Iowa, where it ceases. 
Some detached portions are found in the State of Missouri, and in the environs of Nashville and in 
Perry county, Tennessee. This formation has not been verified further west than the Red Cedar 
valley of low'a ; during my explorations in New' Mexico and the Rocky mountains I found none of 
the strata, but among the spurs of the Sierra de Mogoyon or Sierra Blanca, I met with beds of 
red sandstone lying under the Mountain Limestone; these might belong to the Devonian period, 
hut it is doubtful as I was unable to discover any fossils. 
Lower Carboniferous or Mountain Limestone. — The Low'er Carboniferous has everywhere the same 
characters, whether in Europe, Asia, the two Americas or Australia, and oilers the most beauti- 
ful geognostlcal horizon to be met with in North America. Its strata always consist of hard gray- 
ish limestone, well stratilied and containing numerous marine fossils. It extends almost without 
interruption from Cape Breton to Vancouver island, with a .lithological character almost identical, 
at least with very slight variation , and containing the same fossils, the most characteristic of which 
are the following: Terehratula plano-suicata , Ter. sublilita: Spirifer striatus , Sp. Imeatus; Orthis crenistria- 
Product us semi-reticulatus , Pr. Cora. Pr. Flemingii , Pr. pyxidiformis , Pr . punctatus . Pr. costatus, Pr. pustu— 
