412 CHARLES S. PROSSER 



of mainly thin-bedded sandstone reddish in color or gray mot- 

 tled with red; (6) 12 to 15 feet of massive sandstone in beds 

 from one to several feet in thickness' and varying in color from 

 reddish to grayish ; (7) at the top 7^ feet of a hard massive- 

 bedded and compact white quartzose sandstone similar to No. i. 

 In some thin sandstones in the upper part of No. 6 occurs the 

 characteristic Medina fossil known as ArtliropJiycus harlani (Con- 

 rad) .' 



Clinton formation. — The largest area of this formation flanks 

 both sides of Wills Mountain extending to the Potomac River, 

 while two other areas flank the southern ends of Evitt's and 

 Tussey's mountains. The formation is composed largely of 

 yellowish-green to reddish shales, but on weathering, the flat 

 surfaces frequently have a scarlet tint. There are blackish 

 shales and thin fossiliferous limestones in its upper part as well 

 as a greenish-gray to reddish sandstone. The most important 

 lithologic character of the formation, however, is the two beds 

 of iron ore, the lower occurring from 120 to 160 feet above its 

 base and consisting of two strata of iron ore separated by a band 

 of greenish-yellow shales from 6 inches to 6 feet thick. The 

 two ore-bearing strata have a thickness of from 10 to 12 feet. 

 At Cumberland the upper bed of iron ore is 270 feet above the 

 lower one, in the midst of a brownish, calcareous sandstone, 

 nearly 3 feet thick which is directly above a massive 5-foot 

 sandstone stratum. There are 9 inches of quite clear, fossilifer- 

 ous iron ore and the overlying greenish shales and thin bands of 

 bluish limestone also contain fossils. The thickness of the for- 

 mation varies from 550 to 600 feet. Fossils are common in the 

 middle and upper portions, some of the species being identical 

 with those of the New York Clinton. The name is derived from 

 the exposures at Clinton, Oneida county, N. Y., where the beds 

 of iron ore have been mined for many years, and the stage is 

 identical with No. V^ of the Pennsylvania survey which is 



'For an excellent account of the Medina formation along the Niagara River, see 

 Bull. N. Y. State Museum, No. 45, 1901, pp. 87-95 and accompanying geological map 

 by Dr. Amadeus W. Grabau. 



