OF NORTH AMERICA 
23 
country, where they are found, an arid and desolate aspect, named by the Mexicans, very ap- 
propriately, Mai Pais. 
Near the culminating point of the Sierra Madre , the Trias is replaced by the Carboniferous Lime- 
stone; then, for a distance of twelve miles, the rocks are eruptive Granite, Gneiss and Mica-schist. 
Beyond , on the western declivity of the Sierra , comes the Carboniferous again , the strata of the 
Trias, and finally the white and yellow sandstones of the Jurassic, with streams of volcanic lava 
in the valleys. Inscription Rocks, and the whole mesa that extends nearly to Zuni, are formed of 
the Jurassic rocks. A stream of lava spreads itself in the valley of Ojo Pescado, and terminates 
three miles from the Pueblo of Zuni. 
The valley of the Pueblo and river of Zuni is of Triassic rocks, formed here, as in the Prai- 
lies, of sandstone and red clay, with dolomite and gypsnm. On the plateau which we cross from 
Zuni to the Colorado Chiquito , and from there till we arrive at a distance of five or six miles from 
the secondary cones of the great volcano of the San Francisco Mountains, we are constantly upon 
the Trias. These rocks are nearly horizontal upon the table-land, after having dipped to the East 
and West near the Sierra Madre, where they are very much upheaved. As we approach the Rio 
Colorado Chiquito , the strata incline to the North at a varying angle whose maximum is fifteen de- 
grees; the heads of the strata looking towards the Sierra of Mogoyon, which is seen forty miles 
to the South. 
Shortly after quitting the Colorado Chiquito (Latitude 35°, 18', 43"; longitude 110°, 49', 56".) 
we found below the last beds of the red clay of the Trias, and, in concordant stratification a 
magnesian or dolomitic limestone, with very regular strata from half a foot to one foot in thick- 
ness. Several beds contain fossils badly preserved, among which I recognized, however, a Nau- 
tilus, a (lasteropoda , and perhaps a Belemnites? This formation, which is placed between the Car- 
boniferous and the Trias , corresponds , without doubt , to the Magnesian Limestone (or Permian^ of 
England , and is a new member which I add to the series of the Secondary Rocks in North America. 
This Magnesian Limestone has only four miles of extent in the place where we crossed it, 
and disappears beneath lava and volcanic ashes. I have observed it further to the West, and it 
appears also eastward to occupy one of the lesser chains of the Sierra de Mogoyon. 
From the Sierra of San Francisco (Latitude 35°, 15', 02"; longitude 111°, 16', 26".) to Cac- 
tus Pass (Latitude 35°, 13', 22"; longitude 113°, 27', 16".), the Geology of the country we passed 
through is very complicated, on account of the immense extinct volcanoes, which have covered 
with their lavas and basaltic streams <) the sedimentary and granitic rocks that primitively formed 
this region. The study of this part of our route was rendered still more difficult by the snow- 
According to the venerable baron Alex, von Humboldt, who has examined specimens of Track We 
that 1 collected in the Sierra of San Francisco and in the Rocky Mountains (Mount Taylor and Cerrito), 
the volcanic rocks of that region (New Mexico) , are formed of Oligoclase and of Amphibole (Hornblende) , 
exactly like the rocks composing the volcanoes of Gunung-Parang at Java, and those of the Canary Is- 
lands (ancient Domite of von Buch.). While the volcanic rocks of Colima and Popocatepetl , Mexico , 
and those of Paste and Cumbal , New Granada , are composed of Oligoclase and of Pyroxene. (See : 
Lettre du baron Alex, de Humboldt a L. Elie de Beaumont; Berlin, 10 Mai 1857, in the: Comptes Rendus de 
I'Acaddmie des Sciences, tome XLIV. page 1067; Paris, 1857.) 
( 
