FEANKLm COUNTY. 603 



All of the samples were taken from the Roberts farm, on the banks 

 of Little Darby and just above the county line. 



The only economical use to which the very limited exposures of the 

 Helderberg series in the county can be turned is to the production 

 of a good quality of lime. The preceding table shows that we find 

 in them the typical magnesian limestone which is so much esteemed as 

 a source of lime in all the districts to the south and west in the State. 

 Several of these analyses are almost identical in character with those of 

 the limestones of Greenfield and Leesburg, in Highland county, which 

 belong to the same formation, and they do not diflfer essentially from 

 those phases of the Niagara formation that are turned to most account 

 for the same purpose, viz., the Springfield, Cedarville and Yellow Springs 

 limestone. It will presently be seen that the county possesses an un- 

 limited supply of lime of a very different character, viz., the hot and 

 quick setting lime derived from true carbonate of lime, froiii which the 

 existing demand is principally met, but it is clearly an advantage to 

 have the magnesian carbonates at hand as well as the true carbonates of 

 lime. Good natural facilities can be found for producing large quan- 

 tities of lime, both above and below Georgesville. 



The courses of the Helderberg limestone are too thin and uneven to 

 be valued for building purposes, especially in the presence of the heavy 

 bed of the Corniferous formation that overlies them. 



Ill, CORNIFEEOUS LIMESTONE. 



1. Straiigraphical relations. — The Corniferous limestone holds a very 

 different place in the geology of the county from the foregoing. It covers 

 a much wider area, is a much thicker formation, has very numerous ex- 

 posures, yields building stone and lime of great value, and is worked 

 very extensively for both purposes. When to this it is added that it is 

 one of the most remarkable store-houses of ancient life in our whole 

 series of rock formations, it will be seen that it possesses every element 

 of geological interest. 



As has been already implied, the whole thickness of the formation ap- 

 pears in Franklin county, but there is no one section that contains every 

 element. The nearest approach to a complete section is found in the east 

 bank of the Scioto, from Dublin northwards to the county line. A few 

 feet are here wanting both at the top and at the bottom of the series. 

 The Waterlime, or Lower Helderberg, is found in the bed of the river, a 

 little to the northward, and it is probably safe to say that a descent of 

 ten feet at several points within the district named, would carry us to 

 the lower boundary of the Corniferous ; while its upper limit, viz., the 



