sides extending southward to what is now the dividing 

 line between Butler and Mercer counties. The termi- 

 nus of the glacier was in the region now known as the 

 Beaver Valley. 



As the mass of ice moved across the surface of the 

 ground, its tremendous weight caused it to push thou- 

 sands of tons of soil before it. Great quantities of rock 

 and other soil material were gathered in its movement 

 and these added to its abrasive surface. The cutting 

 and grinding of this great mass of ice certainly left 

 indelible marks on the landscape over which it passed. 



When the ice began to melt, the soil material at 

 the terminus and along the sides was deposited. The 

 material was left in great bank-like formations called 

 Moraines. As one travels from Butler to Grove City, 

 he passes over the lateral moraine and suddenly 

 emerges from the "flat stone country" of the south into 

 the "round stone country," which marks the glacier's 

 path. In these moraines are to be found the fossil re- 

 mains of Corals, Crinoids and other marine animals 

 that were evidently transported from deposits in 

 Northern New York, where the upper Devonian rocks 

 are nearer the surface. 



The great quantities of water resulting from the 

 melting ice, having an insufficient outlet, backed up 

 the Ohio Valley and formed a large lake in what is 

 now the city of Pittsburgh. That the whole previous 

 drainage system of this region was changed, is shown 

 by excavations in the Schenley District of Pittsburgh. 

 Below the soil deposited by the glacial lake there is 

 revealed the p re-glacial gravel which marks the former 

 bed of the Monongahela River. Prior to the coming 

 of the glacier, the waters for some distance south of 



->:>i 19 >;-.- 



