248 BITUMINOUS COAL STRATA. 
were strong currents of water, depositing only 
coarse sand and pebbles ; in this the waters were 
less disturbed, and often tranquil, and so varied and 
charged with materials as to produce layers of 
sandstone, limestone, shell, coal, and iron ore ; thus 
forming a series of strata some hundred feet in 
thickness, containing rich supplies of the most use- 
ful substances for the necessities and comforts of 
man. During this period must have flourished ex- 
tensive forests of terrestrial plants, as we find their 
remains scattered with great profusion through the 
whole of this series of strata. 
VI. The next division (G) is a rock only a few 
feet in thickness, but so remarkable in its charac- 
ter, so continuous, and requiring conditions for its 
promotion so widely different from those of any 
other rocks in the state, that it deserves special at- 
tention. This rock has been called huhr, from its 
strong resemblance to the buhrstone of the Paris 
Basin, and its use in the construction of millstones, 
to which both have been applied. This rock is 
chiefly composed of silex, but it occasionally con- 
tains some calcareous matter. Unlike others of 
which we have spoken, it seems to have been a 
deposition from waters containing the materials in 
chemical solution. It is characterized by the re- 
mains of molluscous animals. 
VII. This division (H) includes the series of strata 
above the buhr. It consists of alternations of sand- 
stone, limestone, shale, coal, and iron ore, and may 
be considered the upper membekr of the coal forma- 
tion. 
Dr. Hildreth, in his late report on the Geology of 
Ohio, has given a section of 35 distinct strata, which 
lie above the calcareo-siliceous rock marked G in 
the above cut, consisting of sandstones, shales, 
limestones, clays, iron ore, and four beds of coal, 
.altogether amounting to a thickness of over 600 feet. 
