120 CORRELATION OF GEOLOGICAL FAUNAS. [bull. 210. 
argillaceous and arenaceous over the calcareous elements — until the 
former prevailed to the exclusion of the latter. The equivalent strata 
of the limestone would in the second locality appear as shales and 
sandstones; and, for instance, the actual stratigraphical equivalent of 
the Tully limestone in Chenango and Otsego counties may be supposed 
to be twice as thick as the Tully itself and not distinguishable litho- 
logically from what lies below or above it. Such a formation is, strictly 
speaking, but a member, and the reason for separating it from the 
Hamilton formation is the appearance in it of diagnostic species not 
belonging to the general Tropidoleptus carinatus fauna, but which 
immigrated into the region from another fauna. Prosser described 
such a case in Otsego Count} 7 , in section 21, east of Noblesville. The 
rocks are described as "smooth, greenish sandstones, in the midst of 
which are block} 7 shales in which Rhynclionella venustula Hall is 
common ;" a i. e. , a characteristic species of the Tully limestone. Asso- 
ciated with this species are Spirifer (mucrondtus) penned us and Tro- 
[>i<h>h plus ca rina his, two characteristic species of the Hamilton forma- 
tion. The rocks below are bluish shales; those above are arenaceous 
shales. The thin " blocky shales with Rhynchonella venustula (Hypo- 
thyris cuboides)" may be regarded as the attenuated stratigraphical 
equivalent of the Tully limestone, but the facts favor the opinion that 
although this holds the attenuated representative of the fauna of the 
Tully limestone, the ad ual st rat [graphical equivalent of the formation 
includes more or less of the blue shales below and the arenaceous 
shales above. 
An exanqne of the discordance bet ween lithologieal and stratigraph- 
ical equivalency is given 1)}' the Oneonta formation. The Oneonta 
sandstone of Otsego County is shown to occupy the same position in 
the column which the Ithaca formation holds in the section at Ithaca. 
The Oneonta formation is, therefore, the stratigraphical equivalent 
of part of the Ithaca formation, but, lithologically, it is the equivalent 
of the lower Cat skill. In the same way Die Chemung formation of the 
Genesee Valley section is stmtigraphically equivalent to the Catskill 
formation of eastern Pennsylvania, in part, to the Erie shales of Ohio. 
But lithologically the Ohio shales are equivalent to the Portage for- 
mation of New York. A formation, therefore, may be stratigraphically 
equivalent to one portion, while lithologically it is equivalent to 
another portion (either higher or lower) of the geological column. 
CORRELATION OF THE DEVONIAN FORMATIONS OF OHIO, 
WESTERN NEW YORK, AND EASTERN NEW YORK. 
The foregoing proposition may be illustrated by tabulating the 
formations of Ohio, western New York, middle New York, and east- 
ern New York, along a west-east series of outcrops, as shown in PI. I. 
" ( 'lassification and distribution of the Hamilton and Chemung series of central and eastern 
New York: Fifteenth Ann. Rept. State Geologist New York, 1895, Part I, p. 183. 
