382 J. P. Kimball on the Geology of Chihuahua. 
going southwest, is continually getting ‘deeper i in the geological 
section. Passing the water -hole of San Estevan - the base of 
a cliff of cantera, here also a quartzit 
is seen in the gullies. This j is robably a a cemented rubble com- 
mon in Ghihnahie at the base i the can gma 
_limestone, in some places saccharoidal and fossiliferous. Some 
twelve miles from the river, the valley proper of the Rio 
' Grande is reached. In it five or six terraces of gravely 
material, varying from 20 to 100 feet in height, may be 
counted. on adie side. The town of Presidio del Norte is 
situated on the last one of the west side, or ah nearest ok 
. “This is the eta gtianoee = the north of the Sierra 
Rica. At the base of this range near Nugal, which is twenty 
yy from — del-Herteon the Obiktahus road: and there. 
re incorrectly laid down on Fleury’s ma 
heavy DaMRIA alegnie alicstinors vandatinen, g ween, 15° N. W. 
—intercalated with impure calcareous shales, The former is 
exceedingly fossiliferous, furnishing the following Cretaceous, 
forms known in Texas : Exogyra plicata, Scalaria Texant, 
Natica Texana, Lima Wacoensis, er with species of Ostrea, 
a us, Caprina and ee ates and fish teeth. The Sierra 
Rica is ina up of (1) lower calcareous shales and fissile slates; 
(2) blue limestone containing Jnoceramus ; (3) upper fissile cal- 
ee 
