Art. V.] Herrick, Geology of New Mexico. 97 
of the Jemes arroy^ is approached and the marl has been re- 
moved by extensive erosion, the surface is rolling and the sandy 
soil supports little beside a scanty growth of juniper. The 
weathering and erosion of the sandy layers leaves a very char- 
acteristic debris of dark flint and jasper as well as fragments of 
pertified wood. 
The valley of the Rio Puerco, about three miles wide at a 
point west of Albuquerque, is about 725 feet deep and its 
upper course is carved out of Cretaceous sandstone and shales. 
On the west side these strata reach the present river bed at the 
so-called Punta de la Mesa two miles north of the little town of 
San Ignacia which is north-west of Albuquerque. The river 
here seems to occupy the site of an anticline, the strata to the 
southwest, the exposures of which diverge from the river, dip 
to the southwest by a very small angle, while those on the op- 
posite bank dip to the southeast. In fact, this line of flexure 
crosses the strata a few rods from the river, which doubles 
round the point. The most complete exposure at this place is 
about 325 feet high, the lower 250 feet or so being of dark fissile 
shales with sandy layers and concretionary and gypsiferous 
phases. The upper 75 feet or less is of a variable reddish or 
yellowish sandstone with local white sand deposits. The con- 
tinuity of the series is much broken by minor faults so that 
neither the position or dip of the strata is constant over large 
areas and the lithological characters are also quite inconstant. 
The upper nodulary phases of the sandstone in some places are 
quite fossiliferous. Only a short distance below the bottom of 
the sandstone layers is a more or less constant band of carbon- 
aceous shale which in some places becomes a lignite. Still be- 
low this is a zone in which occur large numbers of calcareous 
concretions. Each of these when broken reveals the presence 
of a fossil, generally one of the two fine Goniatites figured later, 
while a few small fossils occur in the shales. To the north of the 
point the escarpments of the rocks described continue to flank 
the immediate valley of the river for many miles. On the east 
3ide the same series is repeated by faulting and reappears to the 
east in successive ridges. In these exposures it often happens 
