Geography of Ohio 195 



that we study to-daj^ represents for the most part the deposits 

 made by the retreating ice sheet. 



Definite ice halts are registered by bands of thickened drift; 

 the country between such morainic bands also bears drift called 

 ''ground moraine," The bands of drift are built up where ice 

 wastage and ice feeding are approximately equal. If, in a year, 

 the front of the glacier is wasted 1000 feet, and the onward move- 

 ment of the ice sheet during this time is also 1000 feet, its margin 

 remains stationary, and the debris in that thousand feet of wasted 

 ice is deposited at the margin. If the feeding of the ice is slightly 

 less than the wastage, the margin retreats slowly and the debris 

 is accumulated in a wider ridge or band. AVe sometimes have 

 morainic bands several miles wide. These represent marked 

 wastage of the ice accompanied by almost as active feeding. 



It has been established that a continuous advance did not 

 characterize the precessional movement of the glacier ; nor did a 

 constant retreat mark its recession; instead, oscillations took 

 place at many points along the margin. For several seasons the 

 front of the ice may have held a nearly constant position; then, 

 during succeeding years, the ice growth being greater than the ice 

 decay, the margin advanced, riding over and eroding deposits just 

 made; or, the wastage being much in excess of the feeding, a 

 corresponding retreat resulted. 



Terminal moraines, retreatal moraines, morainic loops. The 

 farthest advance of any particular ice sheet is marked by the termi- 

 nal moraine of that epoch. Other positions of the margin, lying 

 iceward of this extreme position, are marked b}^ ''retreatal" 

 moraines. All bands of drift between the terminal moraine and 

 the dispersion centers of the ice are retreatal moraines. Small 

 basins and valleys were occupied by lobes and tongues of ice. 

 Along the front and sides of these lobes and tongues debris accumu- 

 lated, forming morainic loops. Morainic loops are details of 

 retreatal and terminal moraines. 



The margin of a continental glacier is always irregular, if there 

 is any appreciable relief in the country which it covers. The 

 movement of the glacier is retarded by increasing altitudes; it 

 moves onward freely into valleys or basins of lower altitudes. 

 Our continental glacier, extending as it did quite across the whole 

 continent, met a great variety of relief. Through the basin of the 

 Mississippi, the ice advanced most easily and extended farthest. 



