142 GEOLOGY OF OHIO. 



Goshen salt well leaves the valley, and on the hills south of the Koko- 

 sing, where it joins the Mohican, on the west line of Coshocton county, 

 the Putnam Hill limestone assumes the character I have described. 



Both the limestones under consideration, like most others contained 

 in the Coal Measures, yield a brown lime on calcination (and yet one 

 which produces an excellent mortar). This is undoubtedly due to the 

 quantity of iron and clay they contain, and is one of the results of 

 their formation in shallow and circumscribed bodies of water, which 

 received the drainage of surrounding land surfaces carrying both iron 

 and clay. 



Another striking characteristic of these and some other limestones of 

 the Coal Measures is the quantity of silex which they locally contain. 

 This is a marked feature in the Zoar limestone, and it becomes so cherty 

 as to be called flint, or buhr-stone, in many parts of Tuscarawas, Coshoc- 

 ton, and Muskingum counties. In other portions of the Alleghany coal 

 field the higher limestones exhibit the same phenomena, and buhr-stone — 

 the calcareo-silicious rock of Hildreth — is met with in a great number of 

 localities in Ohio, West Virginia, and Kentucky, aside from the famous 

 one at Flint Ridge. 



The origin of the silex in these flinty limestones has never been satis- 

 factorily explained. It has sometimes been attributed to hot springs, of 

 which the water contained much silica, but the general distribution of 

 the flint and the immense number of fossils sometimes contained in it, 

 seem to me insurmountable objections to this view. It appears to me more 

 probable that the silica was derived from microscopic organisms, such as 

 the diatoms. It is well known that at the present time very extensive 

 deposits of silicious earth ("infusorial earth") are being made in our 

 lakes and lagoons. These are frequently associated with shell marl and 

 sometimes bog iron ore. In the Tertiary age, even more extensive beds 

 of diatomaceous silica were formed than any belonging to the present 

 age yet discovered, the polishing slate of Bilin ("tripoli"), Monterey 

 and Nevada " infusorial earths," etc.. In the older formations no such 

 strata are found, and yet it is hardly probable that the low forms of life 

 from which these beds of silica are derived are of modern date. From 

 some experiments recently made by Mr. Henry Newton at my request, 

 we learn that the silicious shields of diatoms are more soluble than almost 

 any other form of silica known, and it seems to me quite possible that in 

 the older diatomaceous earths the individual forms have disappeared by 

 solution, and the mass has been converted into compact amorphous silica, 

 such as we find in our beds of chert. I would, therefore, suggest, that in 

 many parts of the lagoons which, from time to time, occupied the coal 



