192 AGE OF THE ORISKANY SANDSTONE. 



ft. in. 



interstratified with thin seams of finer grained lime, 

 holding light yellowish nodules weathering almost 

 white, and thin seams of dark coloured shale with a 



bituminous odour 20 6 



Chert occurs in the light grey limestone which forms the summit 

 of these rocks, in the form of nodules, seams, and miniature dykes. 

 The nodules are found in a few instances only, while the seams and 

 dykes are of frequent occurrence. The upper beds of this rock are 

 also cut by dykes of • sandstone. One of these, nearly a foot in. 

 width, is stretched across the bed of a creek, and is hidden on both 

 sides by the bank. From 12 to 15 feet of it may be seen. They 

 are, however, usually much smaller. 



Above the Oriskany Sandstone occurs the Corniferous Limestone. 

 This consists of beds of limestone containing vast numbers of cherty 

 nodules, or beds of limestone interspersed with seams of chert. 



Nodules of chert every way similar to those of the Corniferoua, 

 are found in the Oriskany Sandstone. 



From these facts we think the following inferences may be very 

 naturally drawn : 1st. That after the Onondaga rocks had been 

 deposited they emerged from the ocean, and the exposure to the 

 weather produced the fissures which are now filled with chert and 

 sandstone forming dykes. — 2nd. That at the time of the submer- 

 gence, there was ushered in a condition favourable to the deposition 

 of chert. The inference that the Onondaga rocks were hardened 

 before the deposition of the sandstone, is also supported by the fact 

 that in some places large quantities of pebbles of Onondaga rock 

 are found in the sandstone. 



The inference that the same state of things existed during the 

 Oriskany Sandstone period that prevailed during the Corniferous age 

 is supported by the fact, that nearly all the Oriskany fossils are 

 found in the Corniferous, and many Corniferous forms are found in 

 the sand. Mr. Billings has described the following species as be- 

 longing alike to both formations: — Atrypa reticularis (Linn); Striclc- 

 landia elongata (Billings) ; Pentacrinus aratus (Conrad) ; Centronella 

 glansfagea (Hall) ; C. tumida (Billings) ; G. Hecate (Billings) ; Sep' 

 tocelia concava (Hall) ; S.Jlahellites (Conrad) ; Ghonetes hemispTierica 

 (Hall) ; Strophomena ampla (Hall) ; S.perplana (Conrad); S. Pater' 

 sona (Hall) ; 8. Inequistriata (Conrad) ; S. rhomhoidalis (Wahlen- 



