6 NEW YORK STATE MUSEUM 



Later, this locality was once more mentioned by Walcott in 

 his paper on the Taconic question, 1 where the outcrop is consid- 

 ered a block of Trenton conglomerate caught on the line of the 

 great fault which passes through the hill and which separates the 

 Cambric and Siluric strata. In the light of the knowledge 

 obtained by Ford and Walcott, it was evidently unfortunate that 

 this locality with its complex relations became the object of con- 

 tention between the early geologists; for, with similar shales, one 

 of Cambric, the other of Siluric age, on opposite flanks of the hill, 

 apparently without any fossils in the immediate neighborhood, 

 the locality was apt to mislead both antagonists. As the writer 

 has demonstrated elsewhere, the Hudson river shales on the east 

 side of the Hudson river belong to the Normans kill zone of grap- 

 tolite shales and are of Trenton age. Graptolites characteristic 

 of this zone have been found at the western edge of the plateau 

 in Eensselaer in a road metal quarry at the corner of High and 2d 

 streets. The assumption of the intercalation of this supposed 

 Trenton conglomerate in the shales which are of Trenton age, 

 would, therefore, involve no serious incongruity; in, fact, a con- 

 glomerate bed with the same fauna, the same kind of pebbles 

 and matrix, has been ■observed by the writer a few miles farther 

 south at the Moordener kill, intercalated in graptolite-bearing 

 shales. The question whether the bed on Rysedorph hill is inter- 

 calated in the shales or is a block thrust up along a fault, is 

 therefore, of no great theoretic importance for our investigation; 

 but it may be stated that the appearance of the isolated bed, 

 which seen from the top is folded on itself, is quite suggestive of 

 its having been carried) along the overthrust fault. Under this 

 assumption, however, it is evident that the conglomerate block 

 can not be far removed from its mother bed, and that the latter 

 must be intercalated in the great mass of Nioirmans kill shales at 

 no great depth. 2 



i Am. jour. sci. 1888. 35 :319. 



2 A. S. Tiffany exhibited at the Washington (1891) and Rochester (1893) meetings of the Geological 

 society of America some fossils from the Rysedorph hill outcrop and published his observations in 

 a small separate paper. In this he considers the bed a Trenton limestone and cites the following 

 fossils: Streptorhynchus filitextum Hall, Leptaena sericea Sow., Orthis dicho- 

 toma Hall, Strophomena alternata Con., S. alternistriata Hall, Asaphusgigas 

 DeKay. 



