344 Tke Ohio Naturalist. [Vol. XIV, No. 8, 



MIDDLE MISSISSIPPIAN UNCONFORMITIES AND CON- 

 GLOMERATES IN NORTHERN OHIO. 



By G. F. Lamb. 

 (Published by permission of the Ohio Geological Survey). 



In northern Ohio there are two unconformities with a con- 

 glomerate associated with each which occur in rock of about 

 middle Mississipian age. The area in which the unconformities 

 and conglomerates have been observed include portions of five 

 contiguous quadrangles — West Salem, Wooster, Massillon, Medina 

 and Akron. 



Two conglomerate beds have long been known in central 

 Ohio and which Herrick recognized as extending northward into 

 this part of the state. His conclusion would appear to be correct, 

 but it is not yet known that these beds at the north lie at exactly 

 the same horizon as those in central Ohio. 



In his report on Wayne county (Ohio Geol. Surv. Vol. Ill, p. 

 539) Read incidentally mentions a stratum filled with quartz 

 pebbles which he observed in a quarry at Wooster. In the sum- 

 mer of 1912, the writer examined this outcrop and noted the 

 presence of the unconformity. Later study at other points led 

 to the discovery of another imconfonnity at the base of the lower 

 conglomerate. The presence of these stratigraphic breaks is 

 evidence of crustal movement in this region in middle Mississip- 

 pian time that may have involved a larger area than is at 

 present known. 



The principal facts may be noted briefly: The lower con- 

 glomerate. The best exposures of the base of this stratum occur 

 on either side of the Killbuck Valley in the western part of the 

 Wooster and eastern part of the West Salem quadrangles. The 

 conglomerate varies in thickness from about two feet to eighteen 

 or twenty feet as found along the Killbuck, but thickens eastward 

 and is thirty to forty-five feet before it passes under cover. The 

 basal one to three feet is virtually a bed of loosely cemented 

 quartz pebbles ranging in size from shot to nearly an inch in di- 

 ameter. They are usually ^ to ^ inch in diameter, well rounded, 

 and quite even in size at any given place. Cobble stones from 

 hard layers of the underlying shale are frequent and often lenticu- 

 lar in shape, ranging in size from two to six inches. The largest 

 one found measured two and one-half feet long by one and one- 

 half feet wide, and over five inches thick, and completely embed- 

 ded in quartz pebbles. 



At every point where the base was well exposed, the pebble 

 and cobble bed rests upon blue shale with the contact sharp and 

 generally with very conspicuous undulations. The remainder 



