580 HISTORICAL GEOLOGY. 



from near the Hudson in eastern New York, westward through the state, and 

 at the Niagara River forms the rapids at Black Rock. Thence, it is con- 

 tinued westward through Ontario to Ohio, across northern Ohio, and to 

 Mackinac in northern Michigan. It thus passes beyond the limits of the 

 Eastern Interior Sea into the Central Interior, where it is widely distributed, 

 occurring in Indiana ; in great force at the Falls of the Ohio, just east of 

 New Albany and Louisville ; also in Illinois and Kentucky ; in eastern Iowa, 

 near Davenport, as a bed of gray to buf£ limestone 150 feet thick, resting on 

 Niagara and Trenton; and in Missouri. 



The limestone is commonly light gray to bluish or buff (lightest, which 

 means purest, to the west) ; occasionally it is blackish and rough from the 

 abundance of hornstone masses, which are left projecting by surface wear. 



Much of the rock abounds in corals, like many reef-rocks of modern 

 coral seas. It exhibits its coral-reef character grandly at the Falls of the 

 Ohio, where the corals are crowded together in great numbers, some standing 

 as they grew, others lying in fragments, as they were broken and heaped 

 up by the waves, branching forms of large and small size mingled with 

 massive kinds of hemispherical and other shapes. Some of the cup corals 

 (Cyathophylloids) are six or seven inches across at top, indicating a coral 

 animal seven or eight inches in diameter. Hemispherical compound corals 

 occur five or six feet in diameter. The various coral-polyps of the era had, 

 beyond doubt, bright and varied coloring, like those of the existing tropics; 

 and the reefs were therefore an almost interminable flower-garden. 



In the Canada-New-England region a limestone made up of corals occurs 

 on Lake Memphremagog, between Vermont and Canada, showing that coral 

 reefs flourished there also ; and other localities exist to the eastward. At 

 Gaspe, a thick limestone formation underlies 7036 feet of Devonian sand- 

 stone ; and about 800 feet of the limestone with 1000 feet or so of the 

 overlying sandstones are referred to the Corniferous period. 



Over the western part of the Continental Interior, beyond the Mississippi, 

 at Paleozoic outcrops, the Carboniferous beds often rest directly on the 

 Lower Silurian, or the Cambrian, with nothing of the Devonian between. 

 This is so at the Black Hills, in Dakota, and in central Texas, and east of 

 the Front Range, in Colorado. Farther west, in the Eureka district, there 

 are 6000 feet of Devonian limestone (Hague). 



In the Wasatch Mountains the Devonian is made by King 2400 feet 

 thick, the lower 1000 feet consisting of the " Ogden quartzyte," and the 

 part above this being the lower portion of the " Wasatch limestone," whose 

 total thickness is 7000 feet. Just north of Montana, in British America, 

 there are 1500 feet of Devonian limestone. 



In California, Devonian limestone and shales occur east of the Sacra- 

 mento in Siskiyou and Shasta Counties (Diller and Schuchert). 



In the northern part of British America Devonian rocks occur along the 

 Mackenzie River (F. B. Meek, from the collection of R. Kennicutt) ; but 

 the fossils yet observed are those only of the Hnniilton and later Devonian, 



