382 The American Geologist. Docember, isss 
two. 'i'o tlu' 7A)\\v charcic'tcrized in part hy this variable (i. 
tacniiicdrii, tlic name Tucumcari shales' is here given, after 
Mount Tucumcari, New Mexico, where the zone of Oryphaia 
tucumcarii was originally discovered by Mr. Jules Marcou. 
These shales are well developed in the vicinity of Otter 
creek, on Thompson creek, and on heads of several smaller 
branches of the Medicine Lodge river. 
They are chiefly clay-shales, and lighter hued, as a whole, 
than the Blue Cut shales, which graduate insensibly into 
them. At their summit, they frequently contain bands and 
concretions of clay-ironstone, in the succession of which, 
premonitory of the immense aggregations of concretions 
that constitute certain parts of the Reeder sandstone of 
Kiowa and Clark counties, the (rri/ph(i'((, now in its maximum 
size, is lost sight of, becoming scarcer and more poorlv pre- 
served before wholly disappearing. 
CORRELATION. 
An order of horizons, incomplete, but roughly resembling 
that seen in the Elk-Otter tract, is found in the western 
extension of the Belvidere beds; but the differentiation, 
whether lithological or paleontological, is there less clearlj" 
expressed. To just what extent the various members of the 
Elk-Otter section are present, and where present can be 
recognized, west of the Medicine Lodge River valley, is still to 
be ascertained. 
The relation of the recently described Mentor beds to the 
upper part of the Kiowa shales is evident]}^ close, but a pre- 
cise understanding of it at present seems difficult owing to 
the apparent absence of (injpha'a from Comanche sediments 
north of the Arkansas river. But the writer would here state 
that, in the light thus far obtained, it seems to him that the 
previously supposed relationship of the Mentor to the Deni- 
soii is probably more apparent than real and should be largeh' 
ascribed to similarity of physico-geographic conditions. 
The Blue Cut shales, and at least the upper part of the 
Black Hill shale, should evidently be correlated approximately 
with the Kiamitia, as has been done by Mr. Stanton, the 
Kiamitia being about equally related to the Fredericksburg 
and the Washita. 
The Tucumcari and the Mentor represent somewhat later 
tluin Kiamitia sedimentation, but both ai-e probably earlier 
