62 GEOLOGY OF OHIO. 



(d) Upper Mercer Clay and Shale.— The Upper Mercer coal (num- 

 ber 3 of the numerical series) is not a seam of economic importance in 

 any part of our coal field. It is not worked in even the the smallest way 

 at more than a single point in the state, viz., Canfield, Mahoning county, 

 where it is known as the Bruce coal. It has here a thickness of about 

 thirty inches. But though generally too thin to be considered, at least 

 under present conditions, as worth mining, it is nevertheless a persistent 

 horizon. There is almost always a few inches of coal at its proper level. 

 Its clay is even more persistent than the coal seam. A bed of light- colored, 

 plastic clay can be found at this level in every county in the state in 

 which it is due. It has been practically worked in but few instances 

 and therefore it is be judged mainly by its outcrops. But it seems 

 safe' to say that the deposits of this age contain a large amount of argil- 

 laceous material of at least fair character. At Haydenville, Hocking county, 

 it is extensively worked under the name of the Mingo Clay. It is one of 

 the most valuable clay deposits of the entire series that is included with- 

 in the Haydenville coal field, the series ranging from the Mercer to the 

 Freeport horizon. As shown by a single analysis, it has thf following 

 composition: (Heed.) 



Silica : 69.92 



Alumina 23.46 



Alkalies 1.4S ' 



Oxide of Iron , 2.00 



Magnesia , .40 



Lime 48 



Water 3.84 



The deposit is eight to ten feet in thickness here. Much can be ex- 

 pected on the Upper Mercer horizon in cross sections of the coal field, 

 when clay comes to be required in larger quantities and in greater 

 variety than the present demands. 



(e)Tionesta Clay. — A- few feet, fifteen t or twenty, above the deposits 

 of the age last named, another valuable bed of clay is sometimes found 

 which can be designated by the name given above. But it must be con- 

 fessed that this horizon is one of the undetermined and therefore of the 

 uncertain horizons of the Conglomerate Coal Measure series. Whatever 

 name shall be decided upon for the deposit, it is certain that a more or 

 less persistent clay formation occurs in many counties of the state, as 

 above described. It is used and valued highly in the Union Furnace 

 works already named. A single analysis cannot, of course, go far toward 

 showing the character of a widespread deposit, but the following results 

 give the general composition of the seam as shown at the point last 

 named. (E. Lovejoy, E. M.) 



