182 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



Creek once discharged westward through the lower course of the East Fork 

 of Little Miami. This may have embraced the entire portion between the 

 old divide crossed by Brush Creek near Fort Hill and another supposed 

 divide located by Tight east of West Union.^ The amount of drift is so 

 great in the region between Brush Creek and the East Fork that few surface 

 indications of the courses of the old drainage lines can be found. 



GREAT- MIAMI RIVER. 

 THE PRESENT SYSTEM. 



The Great Miami is the main drainage system of western Ohio. Near 

 its mouth it receives Whitewater River, which drains an area of about 4 ,500 

 square miles in southeastern Indiana. The Whitewater, however, is here 

 treated as a separate system. Exclusive of the Whitewater, the Great 

 Miami has a drainage area of nearly 4,000 square miles, or about one-tenth 

 of the State of Ohio. Its headwaters are in the divide which separates 

 the Mississippi from the St. Lawrence drainage. It drains the greater part 

 of the Cincinnati arch from that divide south to the Ohio River. 



The main stream has its headwaters about 1,000 feet above tide. Its 

 main eastern tributary, Mad River, heads in a more elevated tract in Logan 

 Count)^, whose highest points exceed 1,500 feet. The source of Mad River, 

 however, is in a valley-like depression, standing about 1,300 feet above 

 tide, which also constitutes the source of Rush Creek, a western tributary of 

 the Scioto. Whitewater River, the main western tributary, heads in the 

 most elevated part of Indiana, at an altitude of nearly 1,200 feet. 



The main stream and its headwater tributaries, as far down as the 

 vicinity of Dayton, flow in comparatively shallow postglacial valleys, 

 with courses largely independent of the old drainage lines, the amount of 

 drift being so great as to completely fill, the old valleys. Mad River, it is 

 true, occupies a broad trough-like valley throughout much of its course, 

 but on its borders there are moraines which cause most of the relief, the 

 immediate bluffs being generally but 20 to 30 feet in height. Furthermore, 

 its course seems to be independent of the old drainage 



Below Dayton the Miami and some of its tributaries occupy old val- 

 leys which were only partially filled with glacial deposits. The work of 

 the present streams is mainly the reexcavation of the A^alleys. In this 



^ Communicated to the writer. 



