LIMESTONE FAUNAS OF MARCELLUS SHALES, NEW YORK OoO 



The main purpose of this paper is to emphasize the fact of the geological in- 

 vestigations made by the writer in the years 1895-1901, during which time he 

 obtained a large assemblage of fossil evidence, both of plants and animals, much 

 of which has been examined by a number of the leading authorities, and their 

 verdict invariably has been in support of the views herein advanced. 



The fifth paper of the session, and the last presented by the author in 

 person, was 



ORIGIN OF THE LIMESTONE FA UNAS OF THE MARCELL US SHALES OF NEW YORK 



BY JOHN M. CLARKE 



[Abstract] 



The dark Marcellus shales carry a fauna whose members show evidence, both in 

 diminutive form and thin shell, of having been surrounded by conditions which 

 evince a shallow and befouled sea. In the common and historic employment of 

 the term Marcellus shales as an expression of a lithologic unit it has been the usage 

 to include therein such slight variations in sedimentation as these black shales may 

 carry with them. There are in the various sections of these beds two well marked 

 limestone banks — the one, nearer the base, known as the Agoniatites limestone, 

 the other, still higher, as the Stafford limestone. These are persistent over very 

 considerable distances, but the former disappears from the strata where the latter 

 makes its first appearance — that is, about the meridian of Flint creek, Ontario 

 county. In eastern New York the Agoniatites limestone rises to a height above 

 the top of the Onondaga limestone of not less than 40 feet. Going westward, it 

 apparently approaches the horizon of the Onondaga, and where it makes its final 

 appearance as a distinct and identifiable stratum, carrying its characteristic fossils, 

 it is less than 10 feet above the Onondaga. From this point westward its position 

 may be traced by the appearance of its fossils, the index species Agoniatites expansus 

 Hall having been found immediately above the summit of the Onondaga limestone 

 at Stony point, south of Buffalo, and actually within the uppermost layers of that 

 limestone at Lime Rock, near Leroy. The fauna of this Agoniatite limestone was 

 evidently an invader from the west, dating from the closing phase of the Onondaga 

 stage. At the time of its appearance the shallow- water Marcellus fauna had in- 

 vaded the Appalachian gulf from the southeast and had occupied the eastern field 

 for a considerable period. Directly in the train of the Agoniatite fauna followed 

 the prenuncial cohorts of the Hamilton fauna. The Agoniatite fauna held the 

 footing it had gained, while the latter yielded to unfavorable conditions and tem- 

 porarily retired from the field. 



The Stafford limestone lies at an elevation of from 20 to 30 feet above the hori- 

 zon of the Agoniatite limestone, and its fauna was an assemblage of typical Ham- 

 ilton species. This was. also an invader of later date from the west and the second 

 preliminary appearance of the Hamilton fauna within the confines of New York 

 state. It reached as far eastward as Ontario county, and then retired or was 

 driven to extinction by the continued prevalence of typical Marcellus conditions. 

 This invasion was thus also unsuccessful, but had the fauna dispersed more widely 

 .and been able to take and keep possession of the ground which it subsequently 

 acquired, Hamilton time and sedimentation would have been a more important 

 element in the New York succession. 



