FRANKLIN COUNTY. 637 
cover a long period of paleozoic time, from which we have, thus far, less 
than a dozen described species. 
The economical uses of the Huron shale are quite limited. It is ap- 
plied, on a small scale, to the making of roads and walks—and where 
no severe use is required, its materials are happily adapted to these pur- 
poses. They make a smooth and dry road bed, which is comparatively 
free from dust. Under heavy use, they wear into blue clay very soon, and 
to this complexion they all come at last. 
The only other important use to which they are here applied, depends 
upon the change last noted.. The clays into which they weather, have 
been found to constitute an excellent material for sewer pipes. The 
North Columbus factory depends chiefly on this source of supply for its 
extensive production. Little or no drift is found on the high ridge just 
east of High street, and wherever the shale has been thus exposed to 
atmospheric agencies, it has been turned into clay to a depth varying 
from two to six feet. The clay varies in color from whitish to yellow and 
blue, and passes by slow gradations into the undecomposed slate. The 
pyrites of the shale is often converted by weathering into sulphuric acid, 
and this has united with the lime derived from the concretions and other 
sources, to form sulphate of lime or gypsum in the clay. Little crystals 
of this substance, or selenite, sometimes occur to such an extent as to 
destroy the value of the clay for manufacturing uses. It does not inter- 
fere so much with the substance of the ware as with its surface. By 
chemical union with the common salt, used as a glaze, it prevents the 
formation of the required surface, leaving the ware lustreless and light 
colored. Such portions of the clay as are found charged with these crys- 
tals, it is necessary to carefully avoid. A large manufacture is based 
upon this geological element. The sales of the North Columbus factory 
have sometimes amounted to $70,000 in a year. 
The Wassall Fire-Clay Works, of the city, also make use, to some extent, 
of these native clays for the same purpose. Both manufacture sewer 
pipe of the best quality. 
It has already been stated that no divisions have been established in 
the Huron shale by which its several sections can be united into one 
general section. The failure toestablish divisions results from two facts: 
The almost absolute uniformity of composition in the whole system, and 
the lack of fossils to characterize any particular horizon. It is highly 
probable that more careful study will detect some marks which will serve 
to identify separated portions of the same horizon. One bed remains to 
be noticed, that can be distinguished lithologically; but it occurs at a 
portion of the series where it can render no service of the kind named 
