352 proceedings of the geological society. 



Medina Sandstone. 



Mineral Character. — Medina Sandstone is usually a red or varie- 

 gated, or grey clayey sandstone, both fine and coarse-grained ; solid 

 and coherent about the parallel of Lake Cayuga, but becoming 

 friable and marly in the west, with an intercalated mass of grey 

 quartzose sandstone which contains fossils. This sandstone presents 

 beautiful examples of oblique lamination, as at Rochester, Medina, 

 and elsewhere, these lines being in some places more strongly 

 marked than those of the stratification (Hall, p. 40). 



Where best developed, as at Medina (Hall, Rep. p. 34, 35), it 

 is in four parts, including the grey band. We begin from above : — 



1 . Red marl and nearly a shaly sandstone, with green spots and 

 bands, — the bands being horizontal, parallel to the strata, or vertical. 

 It is pebbly, black and red in places (Wolcott). 



2. Grey quartzose sandstone, entirely distinct from the mass 

 below. 



3. The lower part of this is a mere repetition of No. 1 (red marl, 

 &c), gradually becoming more sandy west of Genesee River, while 

 in the east this division (No. 3) is more siliceous, the central mass 

 (No. 2) not appearing. 



4. The grey or greenish- grey terminal portion of the mass. This 

 is a variable stratum, argillaceous shale, argillaceous or siliceous 

 sandstone by turns (Shawangunk Grit,, the " grey band " of Eaton, 

 and the Grey Sandstone spoken of just before Oneida Conglomerate). 



There are brine-springs in this group throughout New York 

 (Hall). The mineral character of this group changes gradually, 

 but greatly, as it is traced from east to west. 



Place. — Medina Sandstone has not been recognised east of Oneida 

 County, or Little Falls. It is traced from thence towards Oswego, 

 and then goes, as a narrow band, along the south shore of Lake 

 Ontario to its west end, which it wholly embraces, and then takes a 

 somewhat sinuous north-westerly direction to Lake Huron, where, 

 still narrower, it runs along the north side of the Manitouline Islands, 

 and accompanies in its proper situation the other Silurian strata, as 

 they sweep from the south shore of Lake Superior, down the west 

 side of Lake Michigan ; a total course of 1 100 miles. 



Medina Sandstone is a great constant in this basin. We have only 

 mentioned its northern outcrop. The southern extension from Oneida 

 County, our starting-place, in a somewhat irregular course west of the 

 Hudson River, and east of (and among) the Alleghanies, is 750 miles 

 long, giving thus a total outcrop of 1850 miles east, north, and 

 west. On the south it is buried everywhere under newer strata — 

 under the Clinton, about Lake Ontario. M. de Verneuil is under an 

 excusable error in stating (Bullet. Soc. Geol. France, 2 ser.vol. iv. p. 

 668) that Medina Sandstone ceases westward within the State of 

 New York. 



Position. — It dips slightly to the south and west. Further to the 

 south, and beyond this State, it partakes fully of the irregularities of po- 

 sition impressed on its associate strata by the post-carboniferous uplift. 



Transition. — Medina Sandstone rests upon the Grey Sandstone, the 



