122 CORRELATION OF GEOLOGICAL FAUNAS. [bull. 210. 
The line marked R is the horizon at which the first well-marked 
red beds appear in the sections on going up, above which the so-called 
Catskill fauna appears. In general, the figures in the columns 
express the thickness in feet assigned to each formation, the names 
of which are placed opposite them as applied in the several regions 
through which the sections pass. 
These facts may be expressed in terms of equivalency, as follows: 
At the base of this particular series, the calcareous Delaware forma- 
tion, in its upper measures, contains traces of the Tropidoleptus fauna. 
In western New York the Hamilton formation is composed of argilla- 
ceous, calcareous shales, and in eastern New York it is arenaceous, 
but not so strongly so as to change the fauna. The black Huron 
shales of Ohio, following the Delaware limestone and shading off 
gradually into the green shales of the Erie, occupy the interval 
which, in western New York, is made up of the Marcellus shale, 
Hamilton, Tully, Genesee, Portage, and some of the Chemung of 
western and central New York. In central New York these find 
their equivalent in the Marcellus, Hamilton, Tully, Genesee. Farther 
east the Tully and Genesee are wanting, as formations, or are repre- 
sented by Hamilton and Sherburne formations. The Ithaca is in part 
represented by the Oneonta, and its upper part is represented by 
the so-called Chemung of Otsego and neighboring counties. The 
Chemung is represented in that region by the Catskill. Still higher 
up, the space from the black Cleveland shale of Ohio up to the Logan 
conglomerate is represented iu western New York and Pennsylvania 
by the upper Chemung, Panama conglomerate, flat-pebble conglomer- 
ate, and beds at Olean holding Spirifer disjunctus, running up to the 
base of the Olean conglomerate. Farther east this interval is made 
up of the "Catskill, and the probabilities are (though the facts to sup- 
port the opinion are not positively in sight, fossils being out of evi- 
dence) that the Pocono and Mauch Chunk are also the representatives 
of this same AYaveiiy group (or a portion of it) of Ohio. 
The second kind of equivalency has regard to the faunal time scale. 
Equivalency of faunas may be illustrated in a definite case by saying 
that the Tropidoleptus fauna may be recognized over a wide territory 
by its dominant species, but this alone is not sufficient to identify the 
formation. For instance, in the case of the Tropidoleptus fauna of 
eastern New York we have airead3 r noted a list of 12 species which 
are dominant throughout the fauna, as exhibited in the different parts 
of the State. These are dominant on the basis of geographical dis- 
tribution, and therefore may be regarded as representative species of 
the Tropidoleptus fauna, not necessarily of the Hamilton formation. 
Nevertheless, when in central and western New York we pass above 
the formation, which is sharpty defined in the sections, both litholog- 
ically and faunally — so there is no possible doubt as to the termina- 
tion of the formation in these western sections — we find that the fauna 
