41 



At the beginning of tlie Niagara epooli the waters of the Central and 

 Eastern Interior Seas -were laden with sediment and beds of bluish-green 

 shales, known as the Niagara shales, and varying in thielaiess from two to 

 forty feet, were first laid down. Owing to gradual changes in the level of 

 the sea bottom, and a consequent shifting of its tides and currents a 

 clearer, deeper water then resulted, within whose depths there existed life 

 of great variety. Corals and bryozoans were especially represented, and 

 from their remains and those of other marine forms were gradually con- 

 structed those beds of gray and buff Niagara limestone, varying in thick- 

 ness from 100 feet along the Ohio River to 440 feet in the northern and 

 northwestern portions of the State. 



Near the close of the Niagara epoch a gradual uprising of a portion of 

 the Eastern and Central Interior Seas took place. From their bottoms 

 there emerged a long peninsula-like strip of land, whose general trend 

 was northwest and southeast. In the former direction it was imperfectly 

 attached to those portions of Wisconsin and Illinois which had come into 

 existence during the Ordovician era. At its lower extremity it merged 

 with that old island of the Cincinnati Uplift wliich had formed the first 

 land of our present State. The surface rocks of the northwestern corner 

 of Indiana, a narrow and probably interrupted strip extending diagonally 

 across the State, a wide area in the central third and a narrower southern 

 prolongation along the western border of the pre-existing Hudson River 

 group, Avere thus, for the first time, brought above the level of the sea. 



It appears that the force which caused this upraising of the Niagara 

 sea floor was more pronounced at certain points than at others, and so 

 caused a number of dome-like ridges or crests resembling true upheavals 

 in the Niagara beds. These domes are present in an area extending from 

 the Illinois line in Newton County, thi'ough the Upper Wabash Valley 

 nearly to the Ohio line, being especially prominent near Wabash, Delphi, 

 Monon, Kentland and other points in the region mentioned. In them the 

 Niagara strata, elsewhere nearly horizontal, are strongly tilted and show 

 other evidence of a true upheaval. These domes were at first probably 

 small islands whose crests remained permanently above the surrounding 

 sea. They thus formed, for a long period, a more or less broken or inter- 

 rupted connection between the larger area of the Niagara to the south- 

 east and that area in northwestern Indiana which was from now on a 

 part of the continent proper. 



