26 GEOLOGY OF OHIO. 



occasionally large sized blocks are found free in the shale. On account 

 of its enduring nature it is often found in those beds of glacial drift that 

 were derived largely from the destruction of the shales. 



Strap-shaped leaves are occasional^ found upon the surfaces of the 

 shale layers. Sometimes they form thin layers of bright coal which de- 

 ceive the ignorant. Fossil rushes, of the genus Calamites, are also occa- 

 sionally met with. 



But the forms already named are of small account, so far as quantity 

 is concerned, when compared with certain microscopic fossils that are, 

 with little doubt, of vegetable origin, and which are accumulated in large 

 amount throughout the black beds of the entire shale formation, compos- 

 ing, sometimes a notable percentage of the substance of the rock, and ap- 

 parently giving origin, to an important extent, to the bituminous charac- 

 ter of the beds. 



The leading forms of these microscopic fossils are translucent, resin- 

 ous discs, ranging in long diameter from one-thirtieth to one-two-hun- 

 dredth of an inch. Several varieties have already been noted, depending 

 upon the size, particular shape and surface markings of these bodies. 



They were first discovered by Mr. B. W. Thomas, an expert micro- 

 scopist, in the water supply of Chicago, which is derived from Lake 

 Michigan, and Mr. Thomas afterwards learned that they were washed by 

 the water from the bowlder clays that compose the banks and bottom of 

 the lake. He found the discs present in fragments of black shale, and 

 also free in the clay which was derived from the comminution of the shale. 



They were afterwards re-discovered in the black shale of Kettle Point- 

 Lake Huron, by Sir William Dawson, who published a description of the 

 form here found under the name Sporangites Huronensis. Sir William 

 counted them at this time the spore-cases of some fycopodiaceous tree. 



The facts pertaining to them have of late been more widely published 

 and the attention of geologists in various parts of the world has been 

 called to these and similar forms, and thus there is promise of a speedy 

 enlargement of our knowledge in regard to them. Sir William Dawson 

 now considers the common forms to be the spore-cases of rhizocarps allied 

 to Salvinia of the present day. This identification would refer these 

 bodies to floating vegetation on the surface of the seas in which the shales 

 were formed and is thus directly in line with the sagacious interpretation 

 of Newberry, who many years ago attributed the origin of these black 

 shales to a Sargasso sea. 



11, The Waverly Group. 



The important mass of sediments of Sub-carboniferous age, which is 

 known in Ohio and in some adjoining states as the Waverfy group, comes 

 next in the column. The name Waverly was given to these strata by the 

 geologists of the hirst survey, from the fact that at Waverly, in the Scioto 

 Valley, excellent sandstone quarries were opened in them, the products of 



