150 GEOLOGY OF OHIO. 
ally the shale bed above Coal No. 6 is thick, and runs up to the next 
seam; but more generally, at a distance of from three to twenty feet, 
comes in a massive sandstone, which is a marked feature in the Coal 
Measure series. In Pennsylvania this is called the Mahoning sandstone, 
and is a conspicuous and much used landmark in all descriptions of the 
stratigraphic geology of that region. It is there made the dividing line 
between the Lower Coal Series and the Barren Measures. In Ohio it is 
not quite so important an element in the geological column, but it is 
still of sufficient consequence to deserve special notice. It is usually a 
coarse, brown or yellow sandrock, holding the same relations to Coal No. 6 
that the Massillon sandstone does to Coal No. 1, and it is evidently the 
product of a similar change of physical condition. Like the Massillon 
sandstone, too, it occasionally dips down and cuts out the coal along the 
line of the currents of water by which its materials were distributed. 
The Mahoning sandstone is, however, distinguished from its lower rep- 
resentative by being occasionally a conglomerate, a character which f 
‘have never seen the Massillon sandstone assume. The quartz pebbles 
of the Mahoning sandstone are usually small—from the size of a grain 
of wheat to that of a bean—rarely becoming as large as a cherry. This 
will serve to distinguish it from the Carboniferous Conglomerate, which 
lies three hundred feet below, in which the pebbles are sometimes several 
inches in diameter. This will not serve, however, as an infallible diag- 
nostic feature, since some of the sandstones higher in the series—espe- 
cially one over Coal No. 7—occasionally take on this character of the 
Mahoning. The best exibitions of the conglomerate phase of the Ma- 
honing sandstones which have come under my observation are in south- 
eastern Columbiana county, and in northern Tuscarawas county, about 
Zoar. I may say in this connection that, in my judgment, far too much 
importance has been assigned to the Mahoning sandstone as a guide in 
the identification of our coal seams. Though very frequently, perhaps 
generally, found over Coal No. 6, it is by no means constant throughout 
even the Ohio portion of the Alleghany coal field; and if it would be © 
unsafe to trust to it as a means of determining the position of the asso- 
ciated strata here, it must be much more so over a larger area. It is 
plainly the effect of causes that were local in their action, and it is far 
less constant and useful as a geological guide than the limestones of the 
Coal Measures, some of which were the products of general submergences, 
and are continuous over very wide areas. The statement that the Ma- 
honing sandstone is common to both the Alleghany and Illinois coal 
fields is rendered improbable by strong a priori reasons, and it has not 
been confirmed by the latest and most careful observations. 
