56 WILLIS T. LEE 
The shells occur about 500 feet below the top of the Red beds as 
exposed in the Canadian escarpment 5 miles to the west. Stanton? 
states that the collection contains two species belonging probably to 
the genus Unio and comparable, though apparently not identical, 
with the species of Unio described by Meek from the Triassic of 
Gallinas Creek, New Mexico, and by Simpson from the Dockum 
beds in western Texas. Regarding the age relations of these inver- 
tebrates, Stanton states that “the occurrence of Unio in these Red 
beds is considered sufficient evidence of their post-Paleozoic age, 
from the fact that the genus is not known to range elsewhere below 
the Mesozoic, and, with the exception of these forms described by 
Meek and Simpson, it has not been recorded in beds older than the 
Jurassic.” 
_ Since the Red beds at no great distance both east and west of 
the Rio Grande region are in part at least Triassic, it is somewhat 
surprising that all of the 2,000 feet or more of the Rio Grande Red 
beds (except the late Cretaceous red series described below) should 
prove to be older than the Permian. It is possible that further 
investigation may reveal the presence of younger Red beds in locali- 
ties not yet examined in the Rio Grande region, but, judging from 
the evidence at hand, it is more probable that, in case Triassic and 
Permian beds were ever deposited in this region, they were eroded 
away prior to the deposition of the Upper Cretaceous sediments. 
A second or younger red series occurs in the Rio Grande valley which 
has sometimes been confused with the Carboniferous Red beds just 
described. It is perhaps best exposed near Elephant Butte, west of 
Engle, N. M., where it consists of shale, sandstone, and conglomerate 
more or less highly colored and several hundred feet thick. It is 
well exposed only where the Rio Grande and its tributary streams 
have eroded into it between the Caballos and Fra Cristobal Moun- 
tains. It is exposed close to a zone of intense faulting, and probably 
for this reason has been erroneously interpreted as a part of the 
older or Carboniferous Red beds brought to the surface by faulting. 
The red sediments at Elephant Butte are very similar in general 
appearance to the Carboniferous Red beds, and might be easily 
mistaken for that formation until examined closely, when they are 
Personal communication. 
