Mesozoic and Ccenozoic Geology and PaUnontology. 337 



extended over the eastern part of the State of Illinois, over Indiana 

 and the western part of Oliio. The overflow had a width of more than 

 300 miles, and from its western margin it followed the streams westerly 

 to the Mississippi, and from its eastern margin to the Ohio, so that 

 its greatest width in these States exceeded 500 miles. This overflow 

 ma}' have been produced by volcanic energies in the Lake Superior 

 region, and occurred as late as the Post-pliocene age. It was the 

 great destroyer of tlie mammoth and the mastodon and other extinct 

 Post-pliocene mammalia. Since that period the lakes have gradually 

 drained themselves to lower levels through the outlet at Lake Ontario, 

 leaving here and there lower lake beaches and terraces. In process of 

 time, Niagara Falls will recede to Lake Erie, and that lake will be 

 drained to its ancient channel, and other beaches and terraces will be 

 left to represent the present height of the lake in the same manner 

 that I have supposed the higher beaches and terraces to represent the 

 former levels. This explanation seems to the author sufficient to 

 account for all the phenomena discovered by the geologists, and it 

 certainly calls to its aid no mythical hypothesis or unknown freaks of 

 nature, but rests upon well-known physical and geological laws. 



It is no small tax upon the imagination to believe that a great sheet 

 of ice, having an existence in the north, ascended the Lanrentian 

 mountains north of these lakes, and then dipped down into the 

 earth, scooping out Lake Superior 900 feet in depth, pulverizing the 

 material, transforming it into gravel, sand and bowlders, scraping ofl? 

 the soil in some places, and scratching the rocks in others, as it 

 ascended the valle\'s to the height of the dividing ridge between the 

 waters that flowed to the north and the south, and precipitating itself 

 into the tributaries of the Ohio, Mississippi and Missouri rivers, and 

 depositing behind it in such even and beautiful distribution the sand 

 and gravel that now fills the ancient valle3's, and forms a vast, almost 

 level plain over the northern parts of Ohio, Indiana and Illinois, and 

 yet did not sweep off" the ancient gravel beaches, in many places, that 

 now mark upon the mountains and hills the ancient shores of vast 

 bodies of water. 



To believe in the glacial theory requires all this stretch of the imagina- 

 tion, and to be a real sound stalwart in the faith, there are many other 

 marvelous things which must be accepted. One of these is described 

 by a PennsAdvania geologist, to account for the drift phenomena of 

 New York. He says : 



" But when the ice front had been melted back to the southerly crest 



