RESUMfi AND FIELD NOTES. 
141 
sable. Granite rose a cristaux de hornblende 
comme au Lac Superieur. On a au Cerrito ou 
nous campons, les cones et couches d’anciens 
volcans ; trachyte et roche pyroxenique, trap. 
XJn poudingue blanchatre recouvre les tra¬ 
chytes horizontalement le long du creek. ' 
Derriere est la sierra Jumez et la Rio Grande. 
Les volcans sont au sud de Santa Fe entre 
Placer et San Domingo et sont nommes Cerri¬ 
tos ainsi que les ranchos ou nous campons. 
3 Octobre.—Du 57' au No. 58'.—A peu de dis¬ 
tance du camp on trouve le rio de Santa Fe qui 
suit une barranca j>endant sept ou huit milles; 
on a des roches pyroxeniques au bord du vol- 
can et le New Red , releve au nord ou horizon¬ 
tal; avec une immense couche de lava trap, re- 
couvrant le tout et formant le top du barranca. 
Quelquefois ce trap est hasaliforme, et il re¬ 
couvre aussi le gres Tertiaire qui est au bord 
du bassin du Rio Grande. On voit dessous 
une breche volcanique formee de roches pyroxe¬ 
niques et autres, roulees des Rocky mountains 
dessous le trap. Des scories de lava de lapilli 
rougeatres tres-legeres; de la dolomie. Les 
cotes des barrancas ont de 250 a 300 pieds 
d’elevation. Ces montagnes d’bier et de ce 
matin sont nominees les Cerritos. 
4 Octobre.—Du No. 58' au No. 59'.—'On suit 
constamment les bords du Rio Grande, avec 
l’alluvion a cailloux assez gros, pas de blocs 
erratiques. Pres de San Felipe, la gorge se 
resserre et on a la lave trap qui couronne le 
sommet de New Red et de gres blanc. De 
P autre cote du Rio Grande on voit cette lave 
noire s’etendant et formant le sommet des 
cliffs. 
5 Octobre.—Du No. 59' au No. 60'.— On suit 
les memes alluvions sableuses, de plus, la val- 
lee s’elargit considerablement et entre Alameda 
et Albuquerque Ton voit de veritables dunes 
de sable 2 ou 3 en succession dans la direction 
du sud au north. 
8 Octobre. —D’Albuquerque au Camp A au- 
Before arriving at the summit of the plateau, 
we stand on a thick diluvium containing an¬ 
gular fragments of small size, and mingled 
with sand and rose-colored granite, with crys¬ 
tals of hornblende, as at Lake Superior. At 
the Cerrito, where we encamped, we found the 
cones and streams of an ancient volcano ; tra¬ 
chyte, pyroxenic rocks, and trap. A whitish 
conglomerate, in horizontal beds, covers the 
trachytes along the creek. The Sierra Jemez 
and the Rio Grande lie beyond these volcanoes ; 
they are south of Santa Fe, between Placers 
and San Domingo, and they are called Cer¬ 
ritos, as well as the ranchos where we camped. 
October 3 .—From Camp No. 57' to Camp 
No. 58'.—A short distance beyond camp 
we found the Santa Fe river, which follows 
a barranca for seven or eight miles. We find 
volcanic rocks at the borders of the volcano, 
and in the north elevated beds of New Red, 
horizontal, with an immense stream of trap- 
pean lava covering the whole, and forming 
the top of the barranca. This trap is some¬ 
times basaltiform, and it also covers the Ter¬ 
tiary sandstone which is at the border of the 
basin of the Rio Grande. We saw under the 
trap a volcanic breccia, formed of pyroxenic 
and other rocks rolled from the Rocky mount¬ 
ains. We saw scoriaceous lava, and a very 
light reddish lapilli, and some dolomite. The 
sides of the barrancas are from 250 to 300 feet 
in elevation. The mountains seen yesterday 
and this morning are named Cerritos. 
October 4 .—From Camp No. 58' to Camp 
No. 59'.—We were constantly upon the bor¬ 
ders of the Rio Grande. The alluvium is rather 
coarse, and there are no erratic blocks. Near 
San Felipe the ravine becomes narrower, and 
we see the trappean lava which crowns the 
summit of the New Red and white sandstone. 
On the other side of the Rio Grande we see 
' this black lava spread out and forming the 
summit of the cliffs. 
October 5.—From Camp No. 59' to Camp 
No. 60'.—We followed the same sandy allu- 
; vions. The valley widens considerably be¬ 
tween Alameda and Albuquerque, and we find 
true sand-dunes, two or three in succession, in 
a north and south direction. 
October 8 .—From Albuquerque to Camp A, 
