Origin of Coal Measures Fire Clays. — Hopkins. m 
(4) Coal zcithonf under elay. — In most cases the coal is 
underlain with clay of some kind, but in many instances it is 
not fire clay in the sense of being highly refractory. In some 
instances there is no under-clay of any kind, but the coal is both 
underlain and overlain by a ferruginous sandstone. While in 
some instances casts of plant roots and stems occur in the un- 
derlying sandstone, it frequently happens that there is no evi- 
dence of vegetable remains nor any of the leaching action of 
the reducing acids. 
In view of the above statements it appears to the writer that 
the occurrence of a not inconsiderable portion of the fire clays 
is better explained by considering them as transported clays 
reduced before deposition. This does not invalidate the com- 
mon supiDOsition that many of the fire clays are formed in situ 
by the action of the vegetation of the coal beds, but not all of 
them are satisfactorily explained in this way. Furthermore, 
the refractory quality of many of the clays has been increased 
probably since the elevation of the land areas by a leaching out 
of the fluxing materials due in part to the topographical posi- 
tion of the beds near the hilltops and in part to a stratigraphical 
position that permits the access of the acidulated waters. 
NOMENCLATURE OF THE CAMBRIAN FORMA- 
TIONS OF THE ST. FRANCOIS MOUNTAINS. 
By Charles R. I-Ceyks. Des Moines. Iowa, 
The group of granite peaks, lying at the eastern end of the 
Ozark highlands and to which the name St. Francois moun- 
tains has been appropriately applied, has surrounding it a 
thick sequence of sandstones and limestones. Regarding the 
geological age of these rocks there has been more or less ex- 
tended discussion. The terranes recognized in the special re- 
port* on the ^line la Motte district have not the same dehmita- 
tion, nor the same names, as those adopted in other descriptions 
of the region. vSome confusion a]5])ears to exist in conse- 
quence. A Ijrief historical statement at this time will embrace 
the reasons for following the nomenclature proi)osed in the 
special report mentioned. 
'Missouri Geological Sur., vol. ix, pt. iv, 1895. 
