Age of Kaiisas-Oklahojiia Red Beds. — Becde. aJ 
The presence of these fossils clearly demonstrates the Per- 
mian age of these rocks, coming as they do from very near 
to the top of the beds. 
Taking this into consideration the thickness of the Per- 
mian in southern Kansas is about 2,300 feet, allowing 1,150 
feet for the Upper Permian f' red-beds), and 1,150 feet for the 
Lower Permian (Wellington, Marion, Chase and Neosho). 
A SHORT DISCUSSION OF THE ORIGIN OF THE 
COAL MEASURES FIRE CLAYS. 
By T. C. Hopkins, Syracuse, N. V. 
Fire clay is one of the terms in common usage that has been 
adopted into geological literature and it is not possible to give 
a scientific definition that would cover its usage by all classes. 
The manufacturers use the term for a highly refractory clay, 
although they probably would not all agree on the degree of re- 
fractoriness that a clay must have to be properly termed a fire 
clay. Professor Wheeler draws the line at 2,500° Fahrenheit ;'■' 
that is, a clay that withstands a temperature of 2,500° 
without fusion may be properly designated a fire clav. The 
coal miner and the clay miner in the coal region use the term 
for all the clays that underlie the coal seams, and likewise for 
all the blue clays of the Coal Measures whether underlying coal 
seams or not. Chemically, fire clay is a nearly pure hydrous 
silicate of alumina; especially must it have a low percentage 
of the so-called fluxing materials, such as the alkalies, alkaline 
earths, and iron oxides. 
From the standpoint of the manufacturer and the chemist 
many of the blue clays and many of the under clays are not 
fire clays at all. On the other hand the interpretation given 
bv the miner and the prospector leaves out a great many of the 
high grade refractory clays which are not blue and do not oc- 
cur in the Coal ?^Ieasures. However, the miners' use of the 
term, as applied to the Coal Measures, is a natural and a con- 
venient one, as it is not always possible to tell in a field exam- 
ination the difference between clays that fuse at 2,500 degrees 
and those that do not. In many of the dififerent geological re- 
ports the term has evidently been used in this way. When the 
* Missouri Geolvf^ical Surrey, vol. xi, p. 133. 
