28 OHIO FOSSILS 



ahead of the ice: moose and even musk-ox and the great mammoths and mastodons. As the ice 

 melted back, these animals retreated northward and their place in Ohio was taken by the ground 

 sloth, now extinct, and other animals, such as the peccary, now living only far to the south. 



As each new ice sheet advanced, it destroyed many of the surface features left by the 

 preceding one. It covered the remainder with more glacial material. Those of the latest and, 

 we hope, final ice sheet have been somewhat modified or masked by erosion and soil-making 

 in the thousands of years since the ice melted. Some of the bones and shells buried in post- 

 glacial deposits we can call fossils, but post-glacial time passes gradually into historic times 

 and it is almost impossible to set a boundary between the two. It is in this shadow zone be- 

 tween the past and the present that the geologic story ends and the historical account begins. 

 Geologic processes continue to shape the land and to preserve in sediments fossil evidence of 

 the times. 



Pleistocene deposits are extremely important economically for the rich soils of Ohio 

 are mostly glacial in origin. When the farm lands of the northwestern two -thirds of the state 

 are compared with the poorer ones of the southern third, we have a striking illustration of the 

 riches brought to us by the glaciers, riches which far overshadow the value of the sands, 

 gravels, and clays derived from Ohio's Pleistocene deposits. 



