TERTIARY SYSTEM. 87 



mont, and the triangular area of 9,000 square miles extending from there to the 

 Ottawa Valley, the marine fossiliferous clays and sand occur at all elevations, as 

 high as 500 feet. They form a coating for New Brunswick, and a continuous belt 

 on the coast of Maine 150 feet above the ocean. The marine species in these clays 

 and sand are such as live at moderate depths, or varying from the littoral zone to 

 200 fathoms. The submergence must therefore have been much more than 600 

 feet, because the shells and bones must have had some depth of water, as well as 

 the clay, to protect them, in order to produce the fossilization, and they received 

 a covering of drift materials sufficient to protect them from the ocean currents, 

 which then swept over that region, and the disintegrating and denuding agencies 

 which have prevailed during the long train of centuries that have since elapsed. 



§ 192. The fresh-water drift surrounds the great central lakes of the continent, 

 spreads out over a large country in British America, and overspreads part of each 

 of the States in the Valley of the Mississippi. This drift consists of clays, gravel, 

 bowlders, and sand, containing no marine organisms, but bearing land vegetation 

 which now flourishes in the same latitude, and fresh-water shells and the bones of ter- 

 restrial animals of the Post-pliocene age. There are beaches surrounding the lakes 

 which show the lakes have occupied much higher levels than they now do, and 

 were stationary for a time at each of these beaches. The terraces and lake deposits 

 of sand and clay in Wisconsin show that Lake Superior stood 600 feet higher 

 than it does now, at one time, in the Post-pliocene age, at which time it could 

 have overflowed nearly the whole country south of it to the Gulf of Mexico. 

 These terraces and lake deposits occur at different elevations surrounding Lakes 

 Michigan, Huron, Erie, and Ontario, showing they were elevated as high as Lake 

 Superior during this period. They have been noticed 750 feet higher than Lake 

 Ontario. Here was then one grand central Post-pliocene lake, several times as 

 large as all of them combined are now. Upon the shores of this lake angular rocks 

 were rolled into bowlders and beaten down to gravel and sand, that formed beaches 

 and terraces, which were subsequently swept south by the overflowing lake, and 

 spread over Western Ohio, Western Kentucky, nearly all of Michigan, Indiana, 

 Illinois, and Mississippi, and the eastern part of the States bordering the Mis- 

 sissipi River on the west. Large bowlders are spread over these States south as 

 far as the Ohio River, though they gradually diminish in size in that direction, and 

 soon the gravel disappears, and only the finer materials are spread over Mississippi 

 and reach to the Gulf. Beneath these clays and sands, where the rocks were de- 

 nuded of their subaerial debris, the surface is frequently scratched and furrowed. 

 This is especially the case where the higher lands were overflowed. The scratches 

 and furrows appear to have been made by shore-ice on the margin of the lake or 

 lakes when occupying different elevations, and by ice carrying angular rocks and 

 bowlders, that were driven against the shores or shallow places. They bear in all 

 directions, and frequently cross each other, which proves they could not have 

 been made by one body, or by any number of bodies moving in the same direction. 



§ 193. Commencing in the lower tier of counties in New York, where the 

 hills are from 600 to 800 feet above the level of the narrow valleys, and extending 

 south over all the highlands of Pennsylvania, Virginia, West Virginia, the Carolinas, 

 Georgia, Alabama, Eastern Kentucky, and Tennessee, and south to the Gulf of 

 Mexico, there is an absolutely driftless area, and the surface rocks are free from 



