FRANKLIN COUNTS'. 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 hed, 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 v;se 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 selfenite, 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 Wassail 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 to establish 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 



