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 that 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 burr-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 burr-stone, 
the calcareo-silicious rock of Hildreth, is met with in a great number of 
localities, aside from the famous one at Flint Ridge, in Ohio, West Vir- 
ginia, and Kentucky. 
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 tothis view. It seems 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 (“tripoli,” the polishing slate of Berlin, 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 
