GEOLOGY AND PALEONTOLOGY OP THE SCHOHARIE VALLEY 231 



the western district, i. e. in the Decewville beds. The brachio- 

 pods on the other hand seem to have appeared first in the Decew- 

 ville beds of the western area and migrated eastward, reaching 

 the Schoharie region in Schoharie time. 1 



Toward the end of Onondaga time came the invasion of the 

 black muds which produced the Marcellus beds and with these 

 the diminutive fauna characteristic of these beds. Clarke holds 

 that the Marcellus fauna invaded this territory " from the south- 

 east along the inner or Appalachian face of the interior sea". 2 

 The fauna together with the black mud sediments appeared in 

 eastern New York before the sedimentation of the Onondaga 



Fig. 187 Diagram showing relation of Onondaga and Marcellus beds. (After Clarke) 

 . a, a', b, Onondaga limestone; c, lower Marcellus shale; d, d\ Agoniatite limestone; 

 e, e', middle Marcellus shale; /, Stafford limestone; y, (/', upper Marcellus shale 



type was completed in western New York. In other words the 

 lower 50 feet of the Marcellus of eastern New York is the 

 depositional equivalent of the upper Onondaga of western New 

 York. Near the end of Onondaga sedimentation in western New 

 York, the eastern region over which black mud was depositing, 

 was invaded by the last of the Onondaga species, followed 

 directly by the " prenuncial cohorts of the Hamilton fauna ". 3 



The sedimentation accompanying this invasion produced the 

 Agoniatite limestones of the Marcellus, which in the western part 

 of the State is a direct successor of the upper Onondaga [fig. 187]. 

 This goniatite fauna flourished in the east central district for 

 a time, after which it was overwhelmed by the recurrent black 

 lrnul deposits, which were again characterized by the typical 

 -Marcellus fauna. A second invasion of Hamilton (vim s occurred 



x The recent discovery of the Schoharie fauna in northern Michigan 

 shows the extensive transgression of the sea at that time. 



2 Clarke, J. M. N. Y. State Mus. Bui. 19. ]». 1 L5. 



3 Clarke, loc. cit. p. L37. 



