230 PALAEOZOIC TIME — UPPER SILURIAN. 



(5 b) ; 3. Clinton epoch, or that of the Clinton group (5 c) ; 4. 

 Niagara epoch, or that of the Niagara shale and limestone (5 d). 



1. ONEIDA EPOCH (5 a). 

 I. Rocks : kinds and distribution. 



In the Interior Continental basin there are no Oneida rocks, except 

 in its northeastern corner. The Oneida conglomerate (5 a, map, 

 p. 170) is the surface-rock in central New York, in Oneida and 

 Oswego counties, and west to Lake Ontario, lying just south of the 

 outcropping Hudson Eiver beds. It is 20 to 120 feet thick in this 

 region. Going eastward, it disappears, being very thin in Herkimer 

 co., and not occurring at all in the Helderberg Mountains south of 

 Albany. In the Appalachian region it has great thickness. In the 

 Shawangunk Mountains, in southeastern New York (which are 

 within this region), the rock is nearly 500 feet thick, and is called 

 the Shawangunk grit. It is still thicker to the southwest, in 

 Pennsylvania, being 700 feet thick in the Kittatinny valley. 

 It continues on through Virginia, following the course of the 

 Appalachians. 



The rock is a hard, gritty conglomerate or sandstone, of a grayish 

 color, made of rounded quartz pebbles and sand, or of coarse sand 

 alone, very firmly cemented. It is so rough in surface as to serve 

 for millstones : the Esopus millstones are made of it. The firm- 

 ness of the rock contrasts strikingly with the loose texture of the 

 Medina sandstones. 



In the Eastern border region, at Anticosti, there are no signs of the 

 Oneida conglomerate ; but, instead, the limestones referred to the 

 Hudson period are followed uninterruptedly by other limestones, 

 which are continued even into the Clinton epoch ; and in this 

 case the Oneida epoch has probably some representation among 

 the beds. But it is more probable, according to recent investiga- 

 tions, that these limestones are wholly Upper Silurian, and belong 

 to the following epochs of the Niagara period. 



In the Shawangunk Mountains there are two systems of joints, trending 

 S. 20° W. and S. 60° E. (Mather). The Ulster lead and copper mine near 

 Redbridge is situated in this rock : it has afforded large masses of galena and 

 copper pyrites, with blende, but is not worked. The Ellenville and Shawangunk 

 mines are others of similar character in the grit. 



II, Life. 



The only known fossils are Fucoids (Sea-weeds) and a few im- 

 perfect, undetermined shells. One of the Fucoids resembles the 



