OF NORTH AMERICA. 
77 
to 400 miles. These chains proceed from the sources of the Little Sioux , in the north-west of the State 
of Iowa; they traverse the Missouri and the Platte a little above the junction of these two rivers, and 
form the limit between the Prairies and the wooded country. In Arkansas we see them most developed 
in the County of Washington, near the towns of Ozark, Van Buren, and Shawnee; Mount Delaware, 
near Fort Arbuckle, is likewise a portion of those mountains. Finally, this system which is traversed 
by the Red river near Preston, proceeds into the northern part of Texas, where it forms the line of 
hills upon the Brazos, Trinity and Colorado rivers. 
The group of Ozark mountains is not pierced in any part by eruptive rocks. It should be con- 
sidered as a second fold of the Alleghanies , which is parallel to the first and at a distance of tvelve hun- 
dred miles. The elevation of these mountains is nowhere very considerable, it varies from 200 to 
1000 feet above the level of the surrounding plains. 
8. Keewenaw Point and Cape Blomidon system. — The Triassic rooks , or more correctly the Acw Red 
Sandstone formation, in point of geographical extension in the United States, act a most important part, 
for they alone cover a third of that immense country, and added to the Carboniferous rocks, they form 
two thirds, leaving only a third of the surface of this portion of the continent to the eruptive rocks, 
and to the other periods of the sedimentary series. The strata of the Trias have been subjected to 
twm special dislocations, one tow'ards the middle of the deposit, and the other at the end. The last is far 
the most important; although the first has made itself perceptible at very wide distances, and with an 
intensity which, though inconsiderable, has produced very important ranges of hills, especially at Lake 
Superior and the Bay of F’undy. 
After having made many observations upon the direction presented by the first dislocation, I arrived 
at an average direction of E. 35° N. to W. 35° S. In many localities, and more especially in the val- 
leys of the Connecticut and New' Jersey, we meet with numerous dykes of trap belonging to this system, 
whose direction is more to the north, sometimes being confounded with the direction of the System of 
the Alleghanies, or even with that of the Green Mountains ; evidently in consequence of crossings which have 
changed the primitive direction of these dykes. In order to obtain the normal direction of this system 
it is necessary to study it at Point Keewenaw, Isle Royale, Thunder Cape, on Lake Superior, or upon 
the two parallel coasts of the Bay of Fundy, at the Capes Split and Blomidon, also at the Islands of 
Magdalen, in the Gulf of S' Lawrence. These dislocations of the strata of lower Now Red Sandstone 
envelope enormous dykes of basaltic trap, which have burst through, and are spread over, capping the 
sedimentary strata. We find in this trap some veins of native copper traversing the dykes perpendicu- 
larly. Besides, we frequently find there all the ores of copper, native silver, and many zcolitic minerals. 
The knowledge of this important .system of Point Keewenaw and Cape Blomidon is entirely due to my 
friend Dr. Charles T. Jackson, a celebrated geologist of Boston , known especially in the scientific world 
for his discovery of anatsthesia by ether. Several American geologists have in vain attempted to refer 
this system of dislocation to the more ancient systems, going so far even as to connect it with the 
System of the Lawrentine mountains. After having investigated the question with the greatest care, and 
in many places, I am entirely of the opinion of Dr. Jackson. 
Guided by the observations of Sir R. 11. Bonnycastle and Logan, I refer to this system several 
dykes of basaltic trap and strata of Red Sandstone, found at Cape S* George, Newfoundland; in the 
Bay dcs Chaleurs, between the river Ristigouche, Richmond and Port Daniel. Besides, from the infor- 
mation which I have received respecting a portion of the mountains surrounding Fort Webster, in the 
Sierra Madre of New-Mexico, I think the dykes of copper-bearing trap which have been worked 
there, at a place called Santa Rita del Cobre, belong to the System of Point Keewenaw and Cape Blomidon. 
I refer also to it the trap dykes of the vicinity of Galisteo and F’ort Defiance (see: Geological Map of 
New Mexico, Plate VIII). 
9. Sierra de Mogoyon system. — In one of the most central and unexplored parts of North America, 
we find a system of mountain chains called by trappers and hunters, Sierra de Mogoyon or Sierra 
