94 HENRY SHALER WILLIAMS 
though it would be difficult to draw a sharp line at the horizon where 
the change takes place. 
The shales of the Nunda and Chemung are similar, but the sand- 
stones of the Nunda are smooth surfaced, often ripple marked, thin 
and tough in texture; while they are soft, rough surfaced, breaking 
up with vertical rather than splintery fracture (“blocky” as I have 
called them), in the Chemung and are often of a lighter color. 
In Hall’s original definition of the formation certain fossils are 
mentioned as charactersitic: ‘The principal ones are a species of 
Delthyris the shell on each side extending into a wing (D. alata?) a 
Leptaena, Orthis, and a species of Avicula or Pterinea,” etc., but we 
find a fuller list given in the final report published in 1844. Still 
more important than this citation of fossils for the purpose of iden- 
tifying the typical characteristics of the formation is the following 
statement: 
Between Elmira and Chemung they are seen at numerous points, but nowhere 
in the county [Chemung] so well as at the Chemung upper Narrows, about 
eleven miles below Elmira. Here the excavation for the road along the margin 
of the river has exposed more than too feet of rocks, containing abundance of 
the characteristic fossils, and in their greatest beauty and perfection. (P. 323.) 
This quotation indicates where may be found the typical repre- 
sentation of the fauna and, since in later papers the author [James 
Hall] lessened his belief in the separateness of the faunas of the 
Ithaca and Chemung, this standard section is important as it enables 
us now to scrutinize it more closely than Hall did and to discover 
the paleontologic marks by which it may be distinguished from the 
fauna underlying it. 
Adopting therefore this section at the upper Chemung Narrows 
as containing the typical Chemung fauna, as recognized at the time 
of the original recognition and naming of the Chemung group by 
James Hall, we may select from the fossils named as characteristic 
of the Chemung group in the final report (1843) those which are 
known to belong to the section of rocks exposed at Chemung Nar- 
rows (Geol. of Fourth Dist., N. Y., pp. 262 ff.). 
The species originally mentioned by Hall as coming from the 
rocks at Chemung and Cayuta Creek? (the latter has been found by 
t Ch.=Chemung; Cy.—Cayuta Creek. 
