672 GEOLOGY OF OHIO. 



referred to this division, though not more than twelve feet are ordi- 

 narily worked. At Holcomb's quarries, below Springfield, thirteen feet 

 are shown in a full section of the series. 



The courses vary in thickness from four to fourteen inches. Those 

 which are most valued for building stone generally range between these 

 extremes. Several of the courses answer a fair purpose for cutting stone. 

 The same qualified commendation can be given to them for flagging. 

 In neither of these respects has there been, as yet, sufficient inducement 

 to^fully develop the capabilities of the beds. But for general masonry 

 they leave little to be desired. Easily raised and dressed, of convenient 

 thickness and of ample surface, they are not surpassed by any stone in 

 the State in economy of use. 



In color they are either blue or drab. The blue courses frequently 

 weather to drab on their exposed edges, but it is by no means certain 

 that the drab beds have all been derived from the blue by this process of 

 weathering. Slight differences in chemical constitution would serve to 

 explain these differences in color. 



,In what has been said of the value of these beds for building stone, it 

 has been, of course, implied that they are durable. Durability cannot, 

 however, be asserted of all the courses without exception. As in Clarke 

 county, the blue beds sometimes prove treacherous, and this important 

 question for each particular course can only be determined by a practical 

 test. The firm and massive appearance of the stone when raised from 

 the quarry furnishes no safe guide in judging of its power to withstand 

 atmospheric agencies. By far the largest portion of the stratum, how- 

 ever, has great excellence in this respect. The drab courses are, almost 

 "without exception, entirely satisfactory. 



The composition of the Springfield stone has been incidentally alluded 

 to. A sample of the blue rock taken from the quarries of W. Sroufe, Esq., 

 of Yellow Springs, gave the following result. (Wormley.) 



Carbonate of lime , 51.10 



Carbonate of magnesia 41.12 



Sand and silica 5.40 



Alumina, with trace of iron 1.40 



99.02 

 A magnesian limestone of France, cited by Vicat as furnishing an ex- 

 cellent hydraulic lime, was, by chance, noticed to have an almost identical 

 composition. Experiments were instituted with reference to hydraulic 

 properties in the stone now under consideration, and it was found to 

 have great energy as a cement. It can scarcely be doubted that these 

 home supplies will come to be utilized at no distant day. Attention is 



