THE SECTION AT SCHOHARIE, NEW YORK 7 



thyris, Scutella, and Upper Pentamerus — 45, 65, 95, 8, and 22 feet thick respectively — 

 are very distinct, the color, texture, and composition of the limestones in the sev- 

 eral divisions being characteristic. Asa whole, the fauna of each division is its own, 

 but some forms pass from the lower Pentamerus to the top, while each division 

 contains a greater or less number of forms found in that below, showing that despite 

 the sharp physical boundaries, there were by no means equally abrupt changes 

 affecting animal life. Indeed, those forms which existed throughout show no 

 differences in shape, size, or markings, such as would enable one to determine the 

 horizon whence they came. This appears to have been the constant condition 

 throughout the Appalachian region as far as Virginia, for the divisions are char- 

 acteristic of the section. 



The contact between Helderberg and Oriskany was not observed anywhere in 

 the neighborhood of Schoharie, but at two points the concealed interval is not 

 more than 18 inches. Apparently the change from one to the other is as abrupt 

 as is possible. The Upper Pentamerus becomes somewhat flaggy in the upper 

 portion, but the rock is a rather pure limestone, crinoidal and containing many 

 cyathophylloid corals. The Oriskany, however, is a hard sandstone, slightly cal- 

 careous and very ferruginous. It is thin at Schoharie, barely 10 feet, and is seldom 

 seen in place, its ferruginous matter causing somewhat rapid decay. The change 

 in composition marks a physical change which sufficed to cause an almost com- 

 plete change in fauna. Only Leptsena rhomboidalis and Eatonia singularis appear 

 to have passed upward from the Helderberg. The former is excessively rare, while 

 the latter is equally rare in the Helderberg. 



Here, again, one finds a striking contrast with the southern sections. Not only 

 is the Oriskany much thicker at the south, but there is also a transition from the 

 Helderberg as gradual as that from the Niagara to the Waterlime at Schoharie. 

 In southern Pennsylvania the transition bed is a silicious limestone, well shown 

 at Hyndman, in Bedford county, and containing Fav.osites helderbergix, along with 

 characteristic Oriskany forms. In Maryland the Oriskany yields fine crinoids, 

 and crinoidal stems are common in Virginia. These are unknown in the Schoharie 

 region. Still further south the upper beds of the Helderberg became sandy, and 

 the admixture of Helderberg forms in the Lower Oriskany is such that the writer 

 during his first study of the region referred the beds to the Helderberg. 



The most notable differences between the sections are the gradual transition be- 

 tween Ordovician and Silurian and between Silurian and Devonian at the south 

 and the equally gradual passage from Niagara to Waterlime at the north. 



Remarks upon Professor Stevenson's paper were made by J. M. Clarke, 

 H. S. Williams, I. C. White, and A. F. Foerste. 



The next paper was read by title : 



THE OZARKIAN AND ITS SIGNIFICANCE IN THEORETIC GEOLOGY 



BY JOSEPH LE CONTE 



This paper is printed in the Journal of Geology, volume vii, pages 

 525-544. 



