Devonian Era in the Ohio Basin. — Claypole. 41 
Contemporaneously with the elevation of New England 
there occurred a depression in that part of the Appalachian 
gulf now occupied by central and in part eastern Pennsylvania 
and extending into adjoining parts of Maryland and Virginia 
to an unknown distance. Here a basin- was developed reach- 
ing, as above mentioned, a depth of not less than 800 feet on 
the Pennsylvania-Maryland state line — the Marcellus black 
shale attaining there, according to Stevenson, a thickness equal 
to that amount. This is the first evidence of instability in the 
region since the long Corniferous peace set in, but it was only 
a forerunner of other and greater changes of the same nature 
'to which it was subject in following days. From this point of 
maximum depth the Marcellus depression diminished on all 
sides, but its eastern limits are undiscoverable inconsequence 
of later disturbances which have utterly effaced them. On the 
west no trace of it can be found in Ohio. The Cincinnati arch 
was almost certainly above water and the conditions prevail- 
ing around its shores were those of Corniferous days, except 
during the interval indicated by the thin band of blue marly 
shale discovered by Prof. Whitfield, which probably marks some 
short sub-period of the Marcellus when erosion was unusually 
rapid and the supply of water and of shale was unusually large, 
so that the latter traveled beyond its former limit to the west- 
ward and brought with it some of the characteristic species of 
the eastern black shales. When the supply of water and of sed- 
iment fell to their normal amount the solid matter was entirely 
deposited in the Pennsylvania basin above described and the 
limestone with its proper fauna regained its former predomi- 
nance in Ohio. 
It is possible, and not at all improbable, that future research 
will bring to light more than one such invasion of the western 
part of the gulf by the eastern sediment and the eastern life 
of the Marcellus as the exposures of the upper limestone in 
Ohio are more critically studied. But there is no ground for 
belief that such invasion ever extended far or lasted long. Even 
before the Devonian strata disappear under the Illinois coal- 
field, most of their distinguishing features are lost and on their 
emergence at its western edge none of the distinctions recog- 
nized in the east can be detected. 
(To be Continued.) 
