532 C. SCHUCHERT SILURIAN FORMATIONS 



everywhere follows a great break in deposition, for all of the higher 

 Niagaran is absent— that is, the equivalent of at least all of the Lockport 

 and Guelph. Overlying the Clinton or the Shawangunk-Medina, in dis- 

 eonformable contact, is a thick shale series that below is usually of a red 

 or pink color, and above passes into calcareous shales or ribbon limestones, 

 the natural cement rocks of the northeastern Appalachian area. The 

 latter, or Cayugan series, appear to go unbroken into the Lower Devonian, 

 and yet where the contact between them is well exposed the Helderbergian 

 is seen to begin with crystalline crinoidal or knobbly limestone, easily 

 distinguishable from the water limestones of the Silurian system. It is 

 probable that this contact is also disconformable, but the break is of far 

 less significance than that between the Clinton and Cayugan. 



Part I 



HISTORICAL STATEMENT 



Mather 2 was the first geologist to describe the Silurian formations of 

 southeastern New York as represented by the Shawangunk conglomerate 

 and the higher red beds, now known as the High Falls shales, but he did 

 not succeed in correlating either with the Silurian of western New York. 

 His conclusion was : "The observations made do not render it certain 

 whether these red rocks are equivalent to the Onondaga salt group [the 

 Salinan of the present paper] or the Medina sandstone ; but it is thought 

 probable, from some of the mineral characters, no fossils having been 

 seen, that they belonged to the epoch of the Medina sandstone, and that 

 the subjacent Shawangunk grit is equivalent to the gray sandstone 

 [=Oswego of the Ordovician] instead of the Oneida conglomerate [now 

 known to be a phase of the Medina] ." 



The formation name Shawangunk was first used by Mather, who based 

 it on the "white rocks" (= Shongum) of the Indians and the mountains 

 of this name that extend from near High Falls, in Ulster County, New 

 York, southwest through Orange County and through New Jersey into 

 Pennsylvania. These strata in the northeast rest with an angular uncon- 

 formity on the Hudson Eiver series of the Ordovician, but south of New 

 York the contacts are conformable. 



Although no fossils were found in the Shawangunk until recent years, 

 by general consent it was held to be the eastern representative of the 

 Medina of western New York. Accordingly the higher red shales, held 

 to be intimately connected with the Shawangunk, were correlated with 

 the Clinton, even though they also had yielded no fossils. These red 



2 Geology of New York, First Dist., 1843, pp. 353-355. 



