44 



feet in thickness: the latter by beds of black or brownish ])ituminous 

 shales, which i-each a known maximum thickness of 195 feet. The 

 waters in which the materials of the Corniferons limestone were depos- 

 ited were clear and comparatively pure, and in them sponges, corals, 

 crinoids, trilobites and lower animal forms existed in great profusion. 

 From the lime secreted by these marine forms the upper and purer beds 

 of the Corniferous rock are mainly composed. The great abundance 

 of coral life during the period is grandly shown at the Falls of the 

 Ohio, opposite Louisville, Kentucky, where the Corniferous beds have 

 a notable outcrop. Here "the corals are crowded together in great num- 

 bers, 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 being mingled with massive kinds of hemispherical and 

 other shapes. Some of the cup corals are six or seven inches across 

 at the 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 formed there- 

 fore a brilliant and almost interminable flower garden." 



Near the close of the Corniferous epoch deposits of silt, mud and 

 sand began to becloud the clear waters and put an end to the life of 

 many marine forms. The upper beds of rock then laid down, known 

 as the Hamilton, contain in places quite a percentage of magnesia and 

 clay, and embody those vast deposits of hydraulic limestone which, in 

 southern Indiana, have been so extensively used in making natural rock 

 cement. 



The Corniferous rock, when raised above the surface and added to 

 the pre-existing land of the State, formed along the western margin 

 of the latter an irregular strip 5 to 40 miles in width, extending from 

 the present bed of the Ohio River at Jeffersonville northward to the 

 present sites of Logansport and Monticello. North of the Wabash it 

 has been found to be the surface rock in a number of the deep bores 

 sunk for oil, but on account of the thick mantle of overlying drift, its 

 exact limits are unknown. It is probable, however, that at the close 

 of the Corniferous epoch a strip 20 miles or more in average width 

 and extending nearly across the State was, in this region, raised above 

 the floor of the old Devonian sea, to become a part of the permanent 

 land of the future State. 



