LOWER SILURIC SHALES OF THE MOHAWK VALLEY 55 



distinctive character and local development of these shales, demands 

 their description under a separate name, as a local member of the 

 Salina series of deposits, whose exact equivalent in the complete 

 Salina series of Central New York is doubtful. 



The main mass of the Brayman shale is an olive or grayish clay 

 rock often alternating with bluish beds and weathering to a lighter 

 color, and having the appearance of a solid mudbank. Concretions 

 of iron pyrites are very abundant and of all sizes, though generally 

 not much larger than a man's fist. The pyrite is commonly an 

 aggregate of crystals, often of considerable size, the cube and 

 pyritohedron being about equally represented. Exposed portions 

 rapidly oxidize changing to an ochery color, and commonly stain 

 the adjoining shales. As already noted, no fossils have yet been 

 found in this formation. 



Near Mix and O'Reilly's quarry northeast of Schoharie, Hart- 

 nagel's measurement showed 27 feet of these shales. This gives a 

 decrease of 13 feet in a distance of 5 miles. At this point, near the 

 crusher, the contact with the underlying sandstone is well exposed, 

 the two series of strata being absolutely conformable. The surface 

 of the sandstone, exposed for several hundred yards, appears to be 

 a perfectly normal deposition surface, and no trace of erosion, such 

 as we might expect if there was an interval covering Lower and 

 Middle Siluric time, is visible. Moreover the sandstone is pyri- 

 tiferous like the shale, and no fragments of the lower rock are found 

 in the Brayman shales. Neither does the surface of the top sand- 

 stone layer show traces of weathering before the deposition of the 

 Brayman shales. 



It is inconceivable that the surface of this sandstone even if worn 

 down to a uniform stratum, should be swept absolutely clean before 

 the shales were deposited, so that no fragments of sandstone are 

 found in the shale. It is clear that all the facts point to the intimate 

 relationship between the upper beds of sandstone and the Brayman 

 shales, making these sandstones of Upper Siluric (Salina) age. 

 The unconformable contact between these sandstones and the Cham- 

 plainic beds (Lorraine) must be looked for some distance down in 

 the sandstone series. 



The most easterly extension of the Brayman shales, so far as has 

 been observed, is according to Hartnagel . . . near Gallupville, 

 5 miles east of Schoharie, showing that the extreme eastern exten- 

 sion of the great Salina beds of New York can not be far from the 

 town of Knox, Albany county, at which place it is quite likely that 

 the Cobleskill slightly overlaps the Salina. Both of these forma- 

 tions are absent at Altamont, a few miles farther east, and the Ron- 

 dout is seen resting directly on the Lorraine beds. 



The age of the shales here considered has been variously judged. 

 The name pyritous or pyritiferous shales was applied to this forma- 

 tion by the early geologists, and since it occurred below the Coral- 

 line or Cobleskill limestone, which was regarded as of Niagara age, 

 and above the Shawangunk grit, which was supposed to be the 



