RESUMfi AND FIELD NOTES. 
151 
dislocation. Au summet d’un ridge on est 
quelques instants sur le gres jaune Jurassique. 
Pres du Camp No. 16' on a des cristaux de 
gypse blanc, repandus dans l’argile et les gres 
ronges. Plateaux a gradin. Diluvium de 
jaspe, silex, grains de granite. 
2 Decembre.—Du No. 16' au No. 17'.—On 
fait 11 miles au sud sud ouest, tout le temps 
sur Vupper Trias ; les assises plongent au nord 
nord ouest sous un angle de 5 a 7 degres. 
Beaucoup d’argile sableuse rouge quelquefois 
ronge brun a la base. Beaucoup d’arbres fos- 
siles ; quelques-uns ont 4 pieds de diametre et 
sont divises par d’un a deux pieds de long, 
siliciesavec de brillantes couleurs, quelques-uns 
ont des cristaux de quartz, tres-clairs sur le 
rond de tronc. Grand ravin avec nombreux 
eboulements, peut-etre au sommet d’une bill 
une roebe trapeenne? Sierra Blanca. Great 
table-land a l’ouest et au nord. 
3 Decembre.—Du No. 17' au No. 18'.—On 
descend les assises du Trias, qui continuent a 
plonger au nord. Notre direction etant ouest 
sud. On trouve une grande quantite d’arbres 
fossiles, passe a l’etat de jaspes et agates a cou- 
leurs tres-brillantes, rouges, jaunes, blanches, 
noires et barrioles. Des arbres presqu’entiers 
se sont vus aujourd’liui dans le sandstone. Ce 
sandstone est dur gris un peu rosatre ; mais 
surtout gris blanc ; dur ; a grande stratifica¬ 
tion, 3 a 6 pieds. Argiles rouges dominant, 
un peu d’argile grise blanchatre a concretions 
rougeatres. On est, je pense, dans la partie 
moyenne de Trias. Pas de Jurassique. Au 
point oil l’on traverse une large rio, il y a dans 
le sandstone des espece de Gardinia , les co- 
quilles sont fracturees et mal conservees; peut- 
etre que plus tard j’en trouverai de meilleures. 
Dans le diluvium ou a un melange de petits cail- 
loux colores, provenant de ces debris d’arbres 
silicifies. Aspect du pays, table-land; allant 
en s’abaissant du cote du cours du Bio Colorado 
Chiquito. Quelques buttes ou cones a tables 
restant dans la plaine au sud de nous. 
5 Decembre.—Du No. 18' au No. 19'.—On fait 
12 miles ouest ouest sud passant la partie infe- 
the second uplift of the third line of disloca¬ 
tion. At the summit of a ridge, we are, for a 
short time, upon the yellow Jurassic sand¬ 
stones. Near Camp No. 75 we found crystals 
of white gypsum distributed on the clays, and 
red sandstone. The plateau rises gradually, 
and we find a diluvium of jasper, silex, and 
grains of garnet. 
December 2 .—From Camp No. 75 to Camp 
No. 76—(11 miles .)—We travelled towards the 
southwest, all of the time on the upper Trias ; 
the strata dip to the N.N.W. at an angle of 
from five to seven degrees. A sandy red clay 
is abundant, and sometimes it is brownish-red 
at the base. Many fossil trees were seen. Some 
of them are four feet in diameter, and are di¬ 
vided into blocks one or two feet long. They 
are silicified, and are brilliantly colored. Some 
of them contain very clear quartz crystals on 
the round part of the trunk. We saw a great 
ravine with numerous land-slips ; perhaps at 
the summit of a hill a trappean rock. Saw 
the Sierra Blanca, and an extensive table-land 
at the west and the north. 
December 3 .—From Camp No. 76 to Camp 
No. 77.—We descended the beds of Trias 
which continue to dip to the north, our direc¬ 
tion being W. S. We found a great quantity 
of fossil trees turned into jasper and agate, 
with very brilliant colors—red, yellow, white, 
and black, and these sometimes combined. 
Trees, almost entire, were seen to-day in the 
sandstone. This sandstone is grey, a little 
pink, but especially whitish-grey ; it is hard, 
and thickly bedded, the layers being from 
three to six feet thick. The red clays predom¬ 
inate, and there is a little whitish-grey clay, 
with reddish concretions. We are, I believe, 
in the middle part of the Trias. No Jurassic. 
At the point where w r e cross a large river, 
there are in the sandstone some species of Car- 
dinia ? The shells are defaced and badly pre¬ 
served. In the diluvium we find a mixture of 
little colored pebbles coming from the wrecks 
of the silicified trees. The country appears as 
a table-land descending towards the bed of the 
Colorado Chiquito ; some buttes or truncated 
cones rest on tlie plain at the south of us. 
December 5 .—From Camp No. 77 to Camp 
No. 78.—We travelled 12 miles W.W.S., 
