242 The American Geologist. October, 1903. 
reaching the genuine Catskill, but usually occurring in beds of 
shale intercalated in the sandstone for several hundred feet 
above its base. It is not possible to set up any dividing plane 
in middle Pennsylvania between these two groups. The transi- 
tion is not abrupt. Red sandstones with fish remains, and 
showing all the typical characters of the Catskill, are followed 
by shales bearing a Chemung fauna, to be again succeeded by 
other red beds and so on, through a mass of several hundred 
feet. Consequently the horizon between the lowest red sand- 
stones with fishes and the highest shale with Chemung fossils 
is inserted in the tables under the name "Chemung-Catskill 
passage-beds" and the corresponding fauna, is likewise inter- 
mediate in its affinities. 
Returning to the base of the column, the presence of a Mar- 
cellus limestone is noted. This is a highly calcareous shale and 
in some parts, a truly argillaceous limestone, not however rich 
enough to be burnt for lime. It lies at the base of the Mar- 
cellus shale and to the west becomes more massive. In some 
places it may be seen in layers eight to twelve inches thick sep- 
arated by a few inches of black shale. Ten or fifteen feet of 
such alternating strata occur in some quarries. To the eastward 
the limestone diminishes. This series is here assigned to the 
Marcellus, because the greater part of its scanty fauna belongs 
in that horizon. But there is more than a possibility that it may 
represent the shore deposits of the Corniferous sea when the 
shale was beginning to overpower the calcareous matter and the 
Marcellus period was approaching. In that case it may be a 
relic of the home of the shale fauna — the area in which they 
lived during the prevalence of uncongenial conditions in the 
clear waters of the Appalachian gulf — a relic of a once more ex- 
tensive stratum along the Atlantic seaboard which has been al- 
most entirely folded and destroyed by the stupendous changes 
that have since come over the region. 
Perhaps the lists here given might be greatly extended did 
time allow more work upon the strata. Although far from ex- 
haustive, the}- will serve to show, when set by the side of the 
corresponding tables from Ohio, the great contrast between the 
faunas of the eastern and the western shores of the gulf of 
Appalachia. 
