Erie flowed northward, but, since the recession of the 

 glacier, they flow southward into the Ohio river drain- 

 age system. The Great Lakes were also formed by the 

 movement and subsequent disappearance of the glacier. 



Other evidences of changes that have taken place 

 in Pennsylvania may be briefly cited. On the summits 

 of Laurel and Chestnut Ridges of the Allegheny 

 Mountains one can find many limestone quarries in 

 which there are the remains of thousands of Brachio- 

 pods and other marine MoUusks, which indicate the 

 former limits of the Atlantic Ocean. 



In the shales associated with the bituminous coal 

 beds of the state, in limestone deposits, and scattered 

 about near the surface of the ground, one can see per- 

 fectly formed fossil remains of plants that no longer 

 exist, such as Tree Ferns, small flowering plants, Cala- 

 mites, and the striking forms of Lepidodendrons and 

 Sigillarids. These latter plants were of endogenous 

 character and grew to heights of over one hundred feet. 

 Their petrified sections are often mistaken for fossil 

 fishes and snakes. These remnants of extinct forms in- 

 dicate that another order existed in times long past. 



In Jefiferson County, near Brookville, the fossil 

 remains of giant cockroaches, which were evidently 

 once abundant, have been found. It is reasonable to 

 assume that the mammals which were slowly develop- 

 ing at the time these forms existed were afifected by the 

 radical changes in topography and climate. 



The fossil beds of Pennsylvania have yielded the 

 remains of Whales, Dolphins, Horses, Elephants, Pec- 

 caries, Tapirs and many other pre-historic animal 

 species. All of these testify to the principle of ever- 



lasting change. 



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