40 



GEOLOGY OF OHIO. 



but that it was ground off by glacial action there can be no doubt. A 

 wood -cut of this interesting specimen is given on the preceding page. 



Scratched bowlders are not uncommon in the Drift of the highlands, 

 and they may be always accepted as evidence that the material in which 

 they are imbedded is glacial Drift. One of these bowlders, peculiar from 

 its size and position, deserves to be mentioned. This is composed of dio- 

 rite, is some three feet in diameter, and is planed on three sides. It lies 

 in a cutting on the Sandusky, Mansfield, and Newark Railroad, three 

 miles south of Mansfield, and 700 feet above the Lake. 



The large unscratched bowlders described above are generally found 

 on the surface. This we might suspect to be merely the result of the 

 washing away of surrounding softer material; but in the great series of 

 excavations which have been made in the construction of our railroads, 

 canals, etc., large bowlders have been rarely met with below the surface, 

 and they are scarcely found in such circumstances any where except in 

 the bowlder clay of the north-west counties. We often see, also, the large 

 surface bowlders resting on the fine, stratified clays which constitute the 

 upper portion of the Erie clay, and on the stratified sands and clays 

 which form the upper part of the Drift. It seems impossible that they 

 should have been brought to such positions by glaciers or currents of 

 water, as either of these agents would have torn up the underlying clays. 

 We also learn, from their relative position, that these bowlders were de- 

 posited at a later date than the most recent stratified beds of the Drift 

 series, and that they were floated to their present resting places. In 

 short, no argument is required to convince any one who will glance at 

 the facts, that these bowlders, and probably the gravel and sand with 

 which they are sometimes accompanied, were floated on icebergs from 

 the north shore of the great fresh-water lake which once filled the lake 

 basin, and that as these icebergs melted, or when they stranded, their 

 loads were discharged on the top of all the Drift deposits which had been 

 laid down in the preceding epochs of the Quaternary age. 



SOUTH SHORE OF INLAND SEA, WITH ICEBERGS. 



Outlet, "with floating and 

 stranded icebergs. 



Iceberg dropping bowlders 

 on drift. 



At the period of the greatest submergence of the land, icebergs un- 

 doubtedly passed through the gaps of the divide, and thus scattered their 



