234 paleozoic time — upper Silurian. 



sylvania, Virginia, and Alabama. The thickness in the first of 

 these States is in some places 2000 feet. 



The rocks in New York and along the northern border of the 

 United States are mostly shaly sandstones or flags and shales, with 

 some layers of limestone. But in the Michigan peninsula, and to 

 the south, limestone predominates. 



The sandstone is often quite hard, and much of it has the surface 

 uneven from knobby and vermiform prominences, some of which 

 are due to Fucoids. 



In many regions, as in central New York, Ohio, and Wisconsin, 

 there are one or more thin beds of red argillaceous iron-ore, called 

 lenticular ore, from the small flattened grains which compose it. 



In the Eastern border region, at Anticosti Island, the limestones 

 of this period are several hundred feet thick. Shales with lime- 

 stone occur in northern Nova Scotia. 



a. Interior Continental basin. — On the Genesee (see fig. 357, p. 231), the Clinton 

 group consists of, — 



(1.) 24 feet of green shale, of which the lower part is shaly sandstone and the 

 upper part an iron-ore bed ; (2.) 14 feet of limestone, called Pentamerus limestone 

 from a characteristic fossil; (3.) 24 feet of green shale; (4.) 18^ feet of limestone, 

 called the upper limestone. 



On the Niagara (see section, fig. 357 A, p. 232), there is only a shale 4 feet 

 thick, without the iron-ore, overlaid by a limestone stratum 25 feet thick, — this 

 limestone corresponding to the three upper divisions, and its upper 20 feet to the 

 upper limestone. To the eastward, in Oneida, Herkimer, and Montgomery 

 counties, the rock is 100 to 200 feet thick, and includes no limestone, though 

 partly calcareous. The group consists of shale and a hard grit or sandstone 

 in two or more alternations, along with Wo beds of the lenticular iron-ore. 

 The flattened grains making up this ore are concretions like those of an oolite. 

 Near Canajoharie — which is not far from its eastern limit — the formation has a 

 thickness of 50 feet. In the town of Starkville, Herkimer co., the rock contains 

 a good bed of gypsum. 



In Ohio, the Clinton group is recognized by its Fucoids, overlying the Blue 

 limestone of Cincinnati. In Wisconsin, the bed of lenticular iron-ore is 6 to 10 

 or even 15 feet thick. 



In Michigan, south of Lake Superior, and about the northeastern shores of 

 Lake Michigan, the rocks are limestone with hard sandstones and shales like 

 those of central New York. The thickness in the peninsula is 51 feet. 



b. Appalachian region. — In Pennsylvania, Professor Rogers divides the rock 

 into (1) a lower slate, which at Bald Eagle Mountain is 700 feet thick ; (2) iron- 

 sandstone, 80 feet in the Kittatinny Mountain; (3) upper slate, 100 to 250 feet; 

 (4) lower shale, 100 to 250 feet; (5) ore-sandstone, 25 to 110 feet; excepting the 

 last, these strata augment in thickness to the northwest; (6) upper shale, 120 

 to 250 feet, which thickens to the northwest; and (7) red shale or marl, 975 

 feet thick, at the Lehigh Water-Gap. The formation spreads across the 

 State " from the northwest flank of the Kittatinny Mountain to the similar 



