FRANKLIN COUNTY. 615 



quite marked by the occurrence of high-colored clays, red and white, 

 that hold the interval between the two formations. 



One peculiar phase of the lower Corniferous imestone, in this region, 

 deserves to be noted here. About twelve or fift m feet above the base of 

 the formation, deposits of a very fine-grained d sharp, silicious sand 

 occur locally. None of these deposits have b ; i noticed in Franklin 

 county ; but just beyond the line, in Jefferson tov-, . ship, Madison county, 

 on the bank of Little Darby Creek, this Corniferous sandstone is found, 

 and there is every reason' to believe that other pockets of it will be 

 found in the vicinity. Facts of the same sort are given in the report on 

 Champaign county; and in northern Ohio, like deposits are known. 

 The sandstone exactly agrees in character with the Hillsboro sandstone, 

 of the Niagara group. That occurs, also, in local deposits, interrupting 

 the continuity of a great limestone formation. 



This Corniferous sandstone has long been known to the plasterers ot 

 the neighborhood. Whenever the finest quality of work was required, 

 recourse was had to the thin layers of sandstone found in the section 

 here referred to. More particular description of the deposit will be found 

 in the report on Madison county. Its composition is ninety-two per 

 cent, of silica, and seven per cent, of lime. 



The Delaware beds appear in this section, also, in the very thin layers 

 that cover the limestone at many points in the quarry. All that was 

 said in regard to this stratum, under the previous section, applies to it 

 as shown here. 



Enough has now been said upon the stratigraphical relations of the 

 Corniferous limestone, to give the reader a fair idea of the formation. 

 Incidental reference has been made, in several' instances, to its chemical 

 composition, and, also, to its paleontology. These topics will now be 

 treated a little more at length. 



2. Chemical Composition. — Under the head of chemical composition, 

 such analyses as are available, will be given. They will be arranged in 

 ascending order, beginning with the lowest beds of the formation. 



Analysis No. 1, is of the heavy course that lies just above low water 

 at Dublin. As has been shown, it belongs very near the lower boundary 

 of the formation. It shows itself to be a magnesian limestone, and this 

 is true, to the same extent, of but few courses in the Corniferous lime- 

 stone of Ohio. It will be remembered that the Waterlime and Niagara 

 groups, which underlie the Corniferous for at least 200 feet of vertical 

 descent, are both magnesian limestones — for the most part, containing 

 more than forty per cent, of carbonate of magnesia. 



All tliL' beds of the Corniferous limestone, have more or less magnesia 



