152 Mastodon Remains in Ohio. 



coal vein is found to be ^[feather-edged," that iy, the vein becomes thin- 

 ner and thinner, until it disappears entirely, and the shales or sand 

 rock overlying the vein are continued, until they rest directly upon the 

 formation underlying the coal, thus demonstrating that the thinning 

 out is not due to any mechanical process of attrition, such as glacial 

 action, or erosion of any khid. And yet there is partial evidence at 

 least, that the formations upon the immediate left bank of the Olen- 

 tangy, at Delaware, were continuous to Logan county, notwithstanding 

 that at the present time the Niagara is in isolated and limited localities 

 the surface rock. If these deposits were continuous at any time in 

 the world's history, then sedimentary deposits from 550 to 600 feet in 

 height have been eroded, or removed between Logan and Delaware 

 counties, the glacial action thus making an island of the eastern half 

 of Logan county. The upper formation of Logan county — the Huron 

 shale — is not found eastward from there until the left l)ank of the 

 Olentangy is attained, in Morrow, Delaware and Franklin counties, 

 and westward, or rather northwestward the outcrop is found at De- 

 fiance, Napoleon, and the south-west corner of Lucas county. At these 

 latter points the shale formation dips to the north-west. At Delaware 

 and Columbus it dips toward the south-east. Logan county may 

 have been the crest of the arch of the anti-clinal axis passing through 

 the State from Cincinnati to the islands in Lake Erie. 



The almost level plateau found between the outcrop of the Huron 

 shale in Central and Northern Ohio, and the State line of Indiana — 

 most undoubtedly the result of glacial action ; glacial striee having been 

 found near Lima, in Allen county, in Montgomery and Preble coun- 

 ties — for want of more perfect drainage necessarily abounded in 

 swamps and morasses ; and these were admirably adapted to the growth 

 of aquatic plants, and their margins abounded with succulent herbage, 

 and which afforded excellent pasturage for the mastodon and other 

 herbivorse. 



Borings made in nearly a hundred of these swamps reveal a very 

 remarkable uniformity in structure or formatiou. Bowlder clay, sand 

 or gravel, or a mixture of all three, rests upon the rock in situ; then 

 a stratum of clay, usually blue or black (if black, the color is usually 

 derived from vegetable matter, — in a few instances this black clay has 

 yielded the black oxide of manganese) ; over this stratum is found a 

 stratum of peat or peaty like substance ; then a stratum of shell 

 marl ; then humus or vegetable mold, intermingled with sand and 

 clay. With one or two exceptions only, either peat or a peaty-like 

 substance and shell marl were found in every swamp in which bor- 

 ings were made. 



