618 KANSAS CITY REVIEW OF SCIENCE. 



almost everywhere by bluffs, which vary in height from 150 to 500 feet, cut 

 through by the entrances of occasional tributaries. 



The bottom of the ancient channel is often 100 feet or more below the present 

 river, which wanders about, from side to side, over the "bottomlands" of the old 

 valley, now partly filled with debris, brought down by the waters themselves, and 

 deposited siiice the time when the pitch of the river began to be diminished. 

 There are two places where the river flows over hard rock. These are at the 

 rapids near the mouth of the DesMoines River, and a little farther up, at Rock 

 Island. These portions of the river do not represent the ancient courses, for 

 subsequent to the Great River Age, according to General Warren, the old chan- 

 nels became closed, and the modern river, being deflected, was unable tore-open 

 its old bed. 



The Missouri River is now the only important tributary of this section of the 

 Mississippi from the west. Like the western tributaries, farther south, it meand- 

 ers over broad bottom lands, which in some places reach a width of ten miles or 

 more, bounded by bluffs. During the period of the culmination, it probably dis- 

 charged nearly as much water as the Upper Mississippi. At that time, there 

 were several other tributaries of no mean size, such as the Des Moines, which 

 filled valleys, one or two miles wide, but now represented only by shrunken 

 streams. 



The most interesting portion of our study refers to the ancient eastern tribu- 

 taries, and the head waters of the great river. 



The greater portion of the Ohio River flows over bottom lands, less exten- 

 sive than those of the west, although bounded by high bluffs. The bed of the 

 ancient valley is now buried to a depth of sometimes a hundred feet or more. 

 However, at Louisville, Ky., the river flows over hard rock, the ancient valley 

 having been filled with river deposits on which that city is built, as shown first 

 by Dr. Newberry, similar to the closing of the old courses of the Mississippi, at 

 Des Moines Rapids and Rock Island. However, the most wonderful changes 

 in the course of the Ohio are farther up the river. Mr. Carll, of Pennsylvania, 

 in 1880, discovered that the Upper Alleghany formerly emptied into Lake Erie, 

 and the following year, I pointed out that not only the Upper Alleghany, but the 

 whole Upper Ohio, formerly emptied into Lake Erie, by the Beaver and Mahon- 

 ing Valleys (reversed), and the Grand River (of Ohio). Therefore, only that 

 portion of the Ohio River from about the Pennsylvania — Ohio State line, sent its 

 waters to the Mexican Gulf, during the Great River Age. 



Other important differences in the river geology of our country were Lake 

 Superior emptying directly into the northern end of Lake Michigan, and Lake 

 Michigan discharging itself, somewhere east of Chicago, into an upper tributary 

 of the Illinois River. Even now, by removing rock to a depth of ten feet, some 

 of the waters of Lake Michigan have been made to flow into the IlHnois, which 

 was formerly a vastly greater river than at present, for the ancient valley was 

 from two to ten miles wide, and very deep, though now largely filled with drift. 



The study of the Upper Ancient Mississippi is the most important of this ad- 



