6 Transactions Texas Academy of Science. [1 1 2] 
in Arizona and Sonora and described by him as the Trincheras and 
Nogales series. Onr study of the locality under discussion, however, 
was too incomplete to warrant any statement regarding them, save that 
already made of their position and extent. 
STRUCTURE. 
The conditions observed indicate that subsequent to the deposition of 
the Upper Cretaceous series the deposits were elevated and a period of 
depredation v followed, during which, in the western part of the area, all 
of the sediments above the line shales of the Eagle Ford were entirely 
removed. Toward the east the amount of erosion is less and less until 
finally we have the Cretaceous series almost entire. I think it probable 
that the uplift which changed the area from one of sedimentation to 
one of erosion was that which produced the east-west system of fractures. 
Succeeding this period of erosion came its resubmergence, preceded, 
accompanied, and possibly- succeeded by volcanic action. Beds of con- 
glomerate were formed in places and covered by deposits of volcanic 
mud or ash, with or without admixture of pebbles from land areas, and 
at times alternating with conglomerates derived almost entirely from 
such source. The eruptives and lava flows which accompanied this were 
those of the northwest-southeast trend and they continued through a 
very long period. 
The movement which succeeded this was that which gave the lines of 
faulting having approximately a north-south course, and to which is due 
the anticlinal of the Lower Cretaceous hills east of Alamo de Caesario. 
The final disturbance, so far as our observations go, is that of the 
northeast-southwest strike which is accompanied by the numerous por- 
phyritic dykes and extrusions. 
The above section shows the relations of the Cretaceous deposits 
between the Alamo de Caesario and a point seveu miles east, near the 
Bishop mine. Our first impression was that the occurrence of the Eagle 
Ford shales, as noticed in some of the valleys, was probably due to 
unconformity of deposition, but it proved to be on account of block 
faulting which was especially well shown at other localities. 
