CRETACEOUS BED OF MESILLA VALLEY. 
169 
that series, and would class it with the posterior deposits—the psamerythic, the lower new red 
sandstone of English geologists, the roth-todt—liegende of Thuringia, the Gres rouge of the 
peneen bed of France, and from its composition “roches a psephitis,” by Cordier. 
The minerals associated with this rock on tnis latitude—gypsum and rock salt—which efflor¬ 
esce on the degraded surface of the horizontal beds, refer it also to this place. 
Further north in the Territory, Mr. Marcou has met with similar rocks, and classed them 
along with the red clay rocks east of the Rio Grande, including the whole under the term Trias. 
I am inclined, however, to the opinion that this bed is older than the trias, and lithologically 
on parallel 32°, it certainly hears no resemblance to the sandstones of Texas, with the excep¬ 
tion of the bed of greenish ferruginous sand found between Dona Ana and the Horse mountains, 
already alluded to, lying unconformable to the elevated sandstones ; there were no strata of creta¬ 
ceous rocks exposed. This bed was observed by chance, while keeping up a dry creek bed to reach 
the hills at a favorable point. The creek had worn its way some 25 feet deep below the general 
level, exposing below the alluvial covering, which was a brownish sand 5 to 6 feet in thickness, 
a layer of greenish sand ferruginous and crumbling under the finger. The bed was horizontal; 
a depth of 16 to 20 feet was exposed, hut its bottom was not reached ; a layer of silicified stems 
lay horizontally in the sand about six feet below the upper surface, and a second layer eight 
feet below the first. Many of these had been washed out and carried down the creek bed. The 
wood was of various sizes, from an inch in diameter to six inches, and from six inches to two 
feet long. Most of the specimens had the external configuration of an equisetum. As this 
horizontal stratum lay on the upper terrace, or the mesa east of the Dona Ana, it can scarcely 
be supposed to dip under the river, which lies one hundred feet below. The present bottom of 
the Rio Grande being well defined on each side by an abrupt ascent from it to the mesa, the 
river may be supposed, therefore, to have worn its way through and removed this bed, leaving 
only these slight traces now observed on tbe upland. 
The silicified stems gathered here were lost in the subsequent transportation. 
22 U 
