Mesozoic and Cenozoic Geology and Paleontology. 233 
extended over the eastern part of the State of Illinois, over Indiana 
and the western part of Ohio. 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 
may have been produced by volcanic energies in the Lake Superioi 
region, and occurred as late as the Post-pliocene age. It was the 
great destroyer of the 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 Laurentian 
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 off 
the soil in some places, and scratching the rocks in others, as it 
ascended the valleys 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 valleys, 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. 
, Lo 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 Pennsylvania 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 
