Correspondence. 355 
pareotly more favorable than at any other western point east of the 
Rocky mountains. 
In my paper on "The Permian system in Kansas," I have referred to 
outcrops of the Salt Plain measures as far northeast as Little Salt 
creek, north of Hazelton, Kansas, and to its having been pierced as a 
rock-salt-bearing formation in a boring at Pratt, still farther northeast- 
ward, in the Cimmaron-Arkansas divide. It apparently gives rise to the 
gi'oup of brine-springs at which salt is being manufactured in a primi- 
tive way by claim-holders on Elm creek in western Greer county, Okla- 
homa,* and to the salt water which has given name to the Salt fork of 
Red river. Its extension much farther southvvestward seems probable, 
though I have not yet determined its jjosition in the Permian section of 
northwestern Texas given by Mr.W. F. Cummins in the second annual 
report of the Texas State Geological Survey. Occurrences described by 
Mr. Cummins in that report (pp. 44G and 447) are so similar to those of 
the Salt Plain formation that I shall be surprised if future exploration 
does not show some of them to belong to it. On the other hand, it is 
practically certain that some of the saline outcrops of the Texas Permi- 
an belong to a lower horizon. 
The Glass Mountain Formation. — The Cedar Hills sandstone of 
my Kansas Permian section has not been satisfactorily identified in 
central Oklahoma, and it is doubtful whether it is possible to distin- 
guish there the lower or theoretically Cedar Hills, part of the beds be- 
tween the Salt Plain and the Cave Creek, from the lower part of the 
Flower-pot shales, which, however in Oklahoma as in Kansas differ 
somewhat from their more specialized upper part. It therefore seems 
necessary to regard all of the beds above the Salt Plain and below the 
Cave Creek as one formation. This may be called the Glass Mountain 
formation. The name refers to the Glass mountains,"]" whose own 
name has been taken from the slabs of selenite (popularly called "isin- 
glass) which there and at intervals elsewhere are strewn upon the out- 
crops of the more characteristic upper portion of the formation (the 
Flower-pot shales), rendering them conspicuous even at great distances 
by their glistening and sparkling appearance. A thickness of about 
160 feet (unrepeated barometric measurement) was obtained for the 
Glass Mountain formation at the great salt spring of Salt creek, where 
the bas(^ and summit of the formation are respectively marked by the 
summit of the Salt Plain saline floor at the head of the spring and by 
the base of the Medicine Lodge gypsum bed. 
*For a knowledge of these springs and other facts of geological interest, I am 
indebted to Mr. S. T. Sayre. Ho describes three large springs on the south side of 
Elm creek where salt is being made. One of tliese, he says, is about six miles east 
of the west lino of Greer county, and the others about half a mile and a mile bo- 
low the first. At spring No. 1, two parties were making salt when he last visit- 
ed tlio place, and at eacli of the other two springs one party. He reports the 
brine as being very strong, at the upper spring at least, forming a thick crust. 
fCalled also the "Gloss mountains," the form being sometimes used in the singu- 
lar. Tli(i nanus is spelled "(ilass" on Interior Department maps of tlio territory 
and on Roessler's map of Texas and Indian Territory (187-1), and "Gloss" on Col- 
ton's map of Texas and Indian Territory. It is pronounced both ways by residents 
of Oklahoma and southern Kansas. 
