644. GEOLOGY OF OHIO. 
no means in equal force. The first named division is by far the most 
important. Each of these will be very briefly treated. 
1. Unstratified Drift, Boulder Clay, Glacial Drift, Till. Of the twenty 
counties belonging to the Third Geological District, none shows this 
most important phase of this anomalous formation so well as Franklin. 
This is doubtless connected with the fact already noted, that the valley 
of the Scioto constitutes a broad and deep furrow through this central 
district of the State. It must therefore have formed a favorable line of 
advance for the glacial agencies. 
The bowlder clay of Franklin county is essentially an unstratified 
deposit. The bulk of its materials is found in a tumultuous and unas- 
sorted condition. There is a noticeable absence of the lines of deposi- 
tion which always characterize beds of clay or sand that have reached 
their resting places through suspension in water. To make the usual 
absence of these lines more conspicuous, there are seams of sand and de- 
posits of clay of limited extent, scattered throughout the formation, that 
conform in all particulars to the normal appearance of aqueous deposits. 
The contrast between the two divisions of the drift depends also upon 
these points, the presence in one, the absence in the other, of the usual 
marks of deposition in water. 
As the name indicates, the composition of the formation is largely 
elay. The clay, however, holds considerable quantities of sand, pebbles 
and bowlders, distributed irregulary throughout its mass. These bowlders 
are so marked a feature of the formation that they deserve a brief des- 
eription. Whenever they are limestone, greenstone in any of its varie- 
ties, fine-grained quartzites or slates, they are almost invariably polished 
and striated. Rocks of this character can receive and preserve such mark- 
ings, while most granites, gneisses and coarse grained rocks generally, are 
unable to do either. The greenstones are the most abundant of these 
polished blocks, and as they are excessively hard, their planed surfaces 
bear impressive testimony to the immense force to which they have been ~ 
subjected. 
Wherever the bowlder clay is shown, these most characteristic blocks 
abound. They are found in great numbers within the limits of the city 
of Columbus. The grading of streets, the construction of sewers, and 
the usual excavations for buildings, all show them abundantly. 
The cut of the Short Line Railroad, just east of Georgesville, as the 
grade rises from the valley of Big Darby, is carried through ten or fifteen 
feet of the bowlder clay, and very striking examples are shown in it of 
this work. Some of the most interesting specimens are blocks of Cor- 
niferous limestone, the sources of which can not be faraway. They show 
