Contributions to Invertebrate Palaeontology. 535 



NOTE ON THE MARCELLUS SHALE AND OTHER MEMBERS OF 

 THE HAMILTON GROUP IN OHIO, AS DETERMINED FROM 

 PALiEONTOLOGICAL EVIDENCE. 



During the early summer of 1878, President Edward Orton wrote, 

 asking if I could spend a few days with him in centi'al and southern 

 Ohio, in an efiTort to ascertain from palseontoloaical evidence, the 

 true horizon of certain layers of rock which had been somewhat of 

 a difficulty to him ; and in the month of August I spent several 

 days with him for that purpose. While making these somewhat 

 hurried observations at a locality about six miles N. W. of Colum- 

 bus, in Perry Township, on the east bank of the Scioto River, we 

 accidentally discovered a thin bed of dark brown shale, somewhat 

 fissile and bituminous in character, in what Prof. Orton had con- 

 sidered as a representative of the Delaware limestone of Delaware, 

 Ohio. The peculiar texture of tlie shales, occurring where I had 

 expected only a light-colored limestone, excited my interest ; and 

 after a few minutes' examination, I discovered that they contain 

 numerous flattened shells of Leiorhynchus limitaris, Yanuxem. I 

 also obtained from them two specimens of Discina minuta, and ex- 

 amples of Lingula Manni Hall ; the two former being well-known 

 and characteristic forms of the Marcellus shales of New York. On 

 examination, we found that these shells, especially the Leiorhyn- 

 chus, extended through a thickness of several feet of the rock, and 

 that the peculiar bituminous character of the shale accompanied 

 them, but with intercalations of thin layers of less bituminous and 

 lighter-colored limestones. Subsequently, at a point nearly oppo- 

 site Dublin, Ohio, some miles north of the above-mentioned locality, 

 the same shale was again recognized in a corresponding horizon, 

 accompanied by the same species, the Leiorhynchus being quite 

 numerous. At a subsequent visit, Mr. Edward Hyatt obtained 

 Discina Lodensis Hall, another New York Marcellus species. At 

 this second locality, immediately above the shale, and while the 

 limestone layers retain much of the bituminous character, the layers 



