HELDEKBERG AT CORNWALL. 



379 



a century ago by Horton and Mather. The discovery of the southern 

 extension of the formation was made early in 1885, when I found that 

 the so-called Trenton limestones south of Newfoundland and at Long- 

 wood and Woodstock were of Upper Silurian age. Slightly later the 

 fossils were discovered at GreeuAvood lake, and last autumn I found 

 them in Pine hill, northeast of Monroe. 



T described^ the Cornwall area in considerable detail in 1886, but a 

 resume of its principal features may be of interest here. 



In figure 3 are shown the relations in this region. The beds have an 

 aggregate thickness of about 40 feet and comprise the lower Shaly lime- 

 stone, Pentamerus limestone, and water-lime members. They present their 

 usual characteristics and faunas, 

 especially the Shaly member, 

 which is very fossiliferous, but 

 are considerably attenuated in 

 thickness. They are exposed 

 for a length of about a mile. 

 The lower members thin out or 

 are faulted down, in the south- 

 ern part of the area, in which 

 the Shaly limestone lies direct- 

 ly on Longwood red shales. 

 Along the contact of this lime- 

 stone and the shales there are 

 local develojnnents of limonite 

 which were Avorked to a small 

 extent some years ago. 1'he 

 Shaly limestone is well exposed 

 in the old ore pits and contains 

 a varied and abundant fauna, which was described in detail in the 

 ])aper mentioned above. The principal exposures in the northern part 

 of the area are in the cut of the Xew York, Ontario and Western 

 railroad. Here tliere are seen fifteen feet of massive, dark drab 

 colored, impure limestone containing Pentamerus galeatus, Atrypa 

 reticularis and some other forms, underlain by 30 feet of thinner bedded, 

 impure, dark-colored Umestone, containing Leperditia alta in their upper 

 beds. 



The Helderberg formation })robal)ly extends around the Oriskany area 

 to the westward, but there are low grounds and drift in that direction 

 and no outcrops were found. To the southward for several miles there 



Figure 'i.— Region west and south of CornwaU Station, 

 New York. 



* On an Area of Upper Silurian Rocks near Cornwall Station, eastern central Orange County, New 

 York : Am. Jour. Sci., .Id ser., vol. x.xxi, pp. 209-216. 



