138 
GEOLOGICAL REPORT-THIRTY-FIFTH PARALLEL. 
la base et formee des couches superieures du 
Trias, l’argile rouge dominant, avec bandes 
vertes et bandes blanches; le rouge etant quel- 
quefois lie de vin, le petit cone a droite est 
entierement forme de ce Keuper, qui resemble 
beaucoup a Brissot. Une coucbe gris bleu de 
1 pied sert de transition et est en contacte avec 
un gres gris et vert. 
En suite on a une enorme coucbe de gres 
jaune tres fin et dur, 60 pieds de hauteur; c’est 
coupe perpendiculairement et forme des cliffs 
non seulement ici, mais tout le long des mon- 
tagnes que nons voyons liier et aujourd’bui. 
Au-dessous on a des assises de gres blanc tres- 
fin, tres faciles a degager et qui ont des mon¬ 
ticules sableuses au pied des assises ; a peu pres 
25 pieds ; puis on a une assise d’argile gris bleu, 
sub-scliisteuse avec Ostrea. La coucbe d’ Ostrea 
dilatata est a 6 polices du banc de white sand¬ 
stone , et a 2 pouces d’epaisseur; les Ostrece sont 
libres ou unies, et il est tres difficile de trouver 
des specimens avec la valve superieure et le 
bord parfait; quelques Ostrea sont dessemines 
un peu plus baut dans la marne, mais elles 
sont rares. Les argiles a Ostrea , ou True Ox¬ 
ford clay , ont 30 pieds ; puis vient un gres a 
pate calcaire, jaune et brillant, tres dur, a 
strata de 5 ou 6 pieds d’epaisseur, qui devient 
entierement calcaire microtant jaune, au som- 
met; enfin sur quelques parties du sommet 
on a un calcaire silicieux blanc, gris, sans fos- 
siles, analogique a celui d’encampment creek. 
Toute la plaine de Plaza Larga n’a pas d’allu¬ 
vions, a peine quelques fragments de calcaire 
et de gres dissemines sur des monticules, ou 
dans Tucumcari creek. Toutes les montagnes 
environnant sont courronee par ce Jurassique 
a Ostrea dilatata , jusqu’au Camp No. 49, ou 
cette partie superieure disparait. Ostrea Mar- 
cbii ou —-[?] 
23 Septembre.—Du No. 50 au No. 51.—-On 
a constamment V upper Trias, argile est gris 
rouge quelque gres gris a la base ; le Llano se 
voit s.ur notre gauclie jusque vers le Camp 51, 
ou il disparait au sud il est entierement forme 
de Trias, le gres blanc et jaune Jurassique est 
Camp No. 48. The base of this mountain is 
formed of the superior beds of the Trias, red 
clays predominating, with green and white 
bands, the red being sometimes wine-colored. 
A small cone on the right is formed entirely 
of this Keuper, which much resembles that of 
Brissot. A greyish-blue bed, one foot thick, 
forms the transition to, and is in contact with, 
a grey and green sandstone. We afterwards 
found an an enormous bed of very hard and 
yellow sandstone, sixty feet in height, and cut 
perpendicularly, forming cliffs not only at this 
place, but along the whole of the mountains 
which we saw yesterday and to-day. Above 
we found beds of very fine white sandstone, 
which are easily separated, and which have 
hillocks of sand about twenty-five feet high at 
their base. We then found a bed of greyish- 
blue clay, sub-schistose, with Ostrea. The bed 
of Ostrea ddatata is six inches from the bank 
of white sandstone, and is two inches thick. 
The Ostrece are separate or united ; but it is 
very difficult to find specimens with the supe¬ 
rior valve and perfect edges. Some specimens 
! are disseminated a little higher in the marl, 
but they are rare. These clays with Ostrea, or 
1 true Oxford clay, have a thickness of thirty 
feet. Then comes a calcareous sandstone, yel¬ 
low and shining ; very hard, with strata five 
or six feet in thickness, which become yellow, 
“ calcaire microtant,” at the summit. Fi¬ 
nally, on some parts of the summit we found a 
greyish-white silicious limestone, without fos¬ 
sils, analogous to that of Encampment creek. 
All the plain of Plaza Larga is without allu¬ 
vium ; there are hardly any fragments of lime¬ 
stone or sandstone disseminated on the hillocks, 
or in Tucumcari creek. 
All the surrounding mountains are crowned 
with Jurassic strata, with Ostrea dilatata, as 
far as Camp No. 49, where that superior por- 
; tion disappears. 1 Ostrea marchii -[?] 
September 23.— From Camp No. 50 to Camp 
No. 51.—We found constantly the upperTrias; 
the clays and sandstones are red, and some- 
i times the sandstone is grey at the base. The 
Llano appears on our left as far as Camp 51, 
where it disappears towards the south. It is 
1 Mr. Marcou here mentions Ostrea marchii in connexion with two or three words which cannot be deciphered. 
