MARCELLUS SHALE. 
377 
23. MARCELLUS SHALE.* 
Lower part of the Pyritiferous rock (Third Graywacke) of Eaton. Marcellus Shale and 
Black Shale of the Annual Reports. 
{Lower part of No. 8, Pennsylvania Survey. Black Slate of the Ohio Reports.) 
[See Sections Plate 7 and Plate 13, No. 3 and 4; also woodcut, page 27.] 
This rock admits of two divisions. The lower is very black, slaty and bituminous, and 
contains iron pyrites in great profusion ; some portions are calcareous, and it is always mark¬ 
ed by one or more courses of concretions or septaria, which are often very large. This 
division terminates upwards by a thin band of limestone, above which the shale is more fissile, 
and gradually passes from black to an olive or dark slate color. 
In general characters the lower part resembles the Utica slate, and is not distinguisha¬ 
ble from the Genesee slate in its general aspect; it is, therefore, more properly a slate than 
a shale, if the distinction is to be continued. For practical purposes, there is little advantage 
in separating the upper division of this shale from the Hamilton group. The line of separa¬ 
tion is nowhere well marked, the change in lithological character being gradual, while some 
of the fossils continue from one to the other. 
The finely levigated mud composing this rock indicates a period of great tranquillity in the 
waters, moved probably only by currents sufficient to transport the materials over the wide 
extent we find them. The nature and condition of the fossils also indicate a quiescent period ; 
for their forms are among the most delicate, and their parts are usually preserved in the 
greatest perfection. In some instances, however, from their great numbers, they are packed 
closely together, and fracture on the separation of the laminae. 
This rock occupies the depression which extends along the southern border of the Cornife- 
rous limestone, and from two to three or four miles south of its outcrop. From its soft and 
destructible nature, it is only exposed in ravines and water courses, and from these situations 
we obtain a knowledge of its characters. The lower part, when long exposed, weathers to 
a brownish or iron rust color, partially from the presence and decomposition of iron pyrites, 
and partially from bituminous matter. In some situations it retains its purely black color, 
and scarcely separates into slaty laminae after long exposure. 
In many places, this rock contains so much bitumen as to give out flame when thrown into 
a fire of hot coals. From this character, and its black color, it has been considered an in- 
* In Ohio, Kentucky and Indiana, a rock possessing the same characters, and apparently holding the same place as this od@, 
is known as the “Black Slate;” and this term seems more appropriate than Shale, since the rock is everywhere slaty in 
structure. In lithological aspect it is undistinguishable from the Genesee slate of New-York; but since the term Shale has 
been adopted, it is followed in this report. 
[Geol. 4tll Dist.] 
23 
