620 GEOLOGY OF OHIO. 
by the circumstance that for 50 miles in some directions there is no other 
developed quarry. To the northeast, north, and northwest the region 
is heavily buried under beds of drift, and consequently building stones 
are inaccessible. The material from the Covington quarries is dis- 
tributed, therefore, very widely. The stripping is light, the drainage 
easy, the quantity and quality of the stone are both excellent; and great 
variety exists in the thickness of the various strata. 
The Covington stone is chiefly used for building and bridge con- 
struction, and it is mostly consumed in Covington, Ohio, and Win- 
chester and Marion, Indiana. Some bridges on the Pan-Handle railroad 
have been constructed from this material. At the town of Covington 
there are six quarries in active operation, as indicated by the table. 
Some of these must soon be given up, for they lie within the city limits, 
and houses are being now constructed in their immediate neighborhood. 
The material resembles that which is quarried at Springfield in 
being porous and easily cut. Of the specimens sent to the museum one 
was blue and one yellow, and upon examination it was found that they 
differed not merely in the circumstance already mentioned, in that the 
blue layers contain unoxidized pyrites and the other hydrous iron 
oxide, but the blue specimen was a dolomite which would not effervesce 
in acids, while the yellow specimen was much more calcareous. In 
microscopic properties this stone presents no peculiarities. It belongs 
to what we have designated as the porphyritic type; that is, it contains 
rhombohedral crystals of dolomite developed in a mass of formless 
grains of calcite. 
In Shelby county the upper portion of the Niagara formation is 
developed, and several quarries have been opened, the products of which 
are almost entirely burned into lime. Building stones can be there 
obtained at any time and in any quantity desired. 
Hancock county is occupied by rocks of the Niagara and Helderberg 
periods, and although the Niagara rocks which from here extend in a 
narrow strip northward to lake Erie appear to be separated from that 
great area of Niagara rocks in which the Springfield and Dayton quarries 
are situated ; they probably extend beneath the Helderberg rocks that 
intervene and form a portion of the same deposit. ‘The rocks quarried 
at Findlay possess characters almost identical with those of the Spring- 
field stones. ‘They possess a rather porous and open structure, are drab 
in color, and occur in courses from 3 to 12 inches in thickness. The 
