CORRELATION WITH EIGHTEEN-MILE CREEK BEDS 103 



shales of the Upper Devonian at Kettle point, less than 15 miles west 

 and but little south of the strike of the beds from Thedford. Thus the 

 Upper Hamilton — that is, the beds above the Encrinal limestone — can 

 not be very much thicker than the portion exposed. 



CORRELATION WITH HAMILTON BEDS OF EIGHTEEN-MILE CREEK 



Turning now to a comparison of the beds of Thedford with those of 

 Eighteen-mile creek, New York, 130 miles to the east, we find that there 

 is a close agreement in the thickness of the formation at the two locali- 

 ties. Well sections, according to Prof. I. P. Bishop * (1895), show the 

 thickness of the combined Hamilton and Marcellus to be 287 feet. The 

 thickness of the Hamilton in that region is only 76 feet, giving a thick- 

 ness of 211 feet for the Marcellus.f Thirty feet of the latter contain a 

 mingled Hamilton and Marcellus fauna, and must be considered as 

 transitional. If this is counted with the Hamilton, we have 106 feet of 

 that formation and 181 feet of Marcellus. A lower Hamilton fauna 

 existed temporarily during the early Marcellus time, while the Stafford 

 limestone was accumulating with a thickness of 8 feet.! 



The upper Hamilton (Moscow shale) of Eighteen-mile creek is 17 feet 

 thick, and is divisible into two distinct faunas, each characterized by a 

 Spirifer not found above or below. The upper fauna is characterized by 

 Spirifer tullius, with which are associated Amboccelia prseumbona and 

 Schizobolus truncatus, both of which are unknown in the other faunas. 

 Leiorhynchus multicostus (= L. laura) is also abundant. This fauna is 

 found in the upper 4 feet of the Moscow shale. 



The next fauna is characterized by Spirifer consobrinus, and is limited 

 to the lower 5 feet of the Moscow shale. In certain layers Amboccelia 

 umbonata is extremely abundant. Between the two faunas are 8 feet of 

 nearly barren shales. 



About 2 feet above the Encrinal limestone and within the zone of 

 Spirifer consobrinus, occurs a thin coral layer to which nearly all the 

 characteristic large rugose corals of this region are confined. Chief 

 among these are Heliophyllum halli and Cystiphyllum vesiculosum. Favo- 

 sites and Craspedophyllum have not been noted, but they occur in the 

 Encrinal limestone, where also a few cup corals occur. Atrypa aspera 

 is abundant and confined to this bed. 



The Encrinal limestone is less than 2 feet thick, and is characterized 

 by a fauna of over 60 species. Of these, 19 are so far known to be 

 restricted to this bed, though a number of others are among the char- 



* Structural and Economical Geology of Erie County, p. 390. 



fGrabau, 1898 (3). 



t J. M. Clarke and Elvira Wood, Bull. 49, N. Y. State Museum, 1901. 



