98 The Waverly Group in Ohio — Herrick . 
enormous interval, during which in most parts of the northern 
hemisphere there were remarkable disturbances. A slender 
thread of history piloting us through an epoch of disturbance 
and extermination must be most valuable. 
Nevertheless, we are somewhat disturbed by the fact that, 
except for 100 feet of the Erie shale, only seen for a short dis¬ 
tance along the north-eastern margin of the Waverly domain, 
the Chemung is apparently absent. The fact that the Bedford 
shale with an almost Hamilton fauna rests upon this shale still* 
further complicates the matter. It is not possible in the 
limited space here afforded to discuss the reasoning employed, 
but we may simply indicate the conclusions tentatively ad¬ 
vanced. 
Notice first, however, a few points concerning the Chemung. 
Its area is different from that of the Waverly. It is a littoral 
formation. Where its western edge is interstratitled with the 
Waverly is a sudden change of dip—instead of N. E. it becomes 
S. E. Its strata thicken towards the N. E., while those of the 
Waverly grow thicker southward. The Chemung has no 
Lingulae, no trilobites, and its own fauna is one-sided and tickle 
in distribution. Our suggestion is that in time the Chemung 
in New York was equivalent to a continued Hamilton facies in 
Ohio. That the Bedford shale was such a belated member of a 
fauna preserved in the quiet weedy sea of Ohio after New York 
had been the scene of a sudden but one-sided development due 
to changing conditions. That littoral conditions are competent 
to greatly disturb the fauna is plainly shown within the 
Waverly domain. Thus to the east, in the Cuyahoga shales, 
the Devonian Atrypa reticularis and Strophomena rhomboid- 
alis rise into association with species of the highest horizon 
{Keokuk) while in western Ohio they do not pass the littoral 
middle Waverly. The lower part of the Waverly, if we 
correctly read, contains a faunal but not an exact chronological 
equivalent of the upper Chemung. Here, then, we may expect 
to trace the gradual evolution of types exterminated by the 
conflicting conditions in New York. In fact we find a striking 
confirmation of the hypothesis. A complete succession of 
trilobites, including the Devonian genus Fhcethonides of the 
Hamilton in several species, several species of Proefcus and one 
of Dalmanites or Ceraurus , in the lower portions, followed by 
