SURFACE GEOLOGY. 207 
Ohio, or the shallows of the prairie region of Indiana, Illi- 
nois, and Iowa; there melting away and depositing their 
entire loads,—as I have sometimes seen them, a thousand or 
more boulders on a few acres, resting on the Erie clays and 
looking in the distance like flocks of sheep,—or dropping 
here and there a stone and floating on, east or west, till wholly 
dissipated. 
These boulders include representatives of nearly all the 
rocks of the Lake Superior country, conspicuous among 
which are granites with rose-colored orthoclase, gray gneiss, 
and distbed all characteristic of the Laurentian series; 
hornblendie rocks, massive or schistose, and dark greenish 
or bluish silicious slates, probably from the Huronian ; dolo- 
rites and masses of native copper, apparently from the 
Keweenaw Point copper region. 
In the Drift gravels I have found pebbles and small boul- 
ders of nearly all the paleozoic rocks of the lake basin, con- 
taining their characteristic fossils, namely, the Calciferous 
Sandrock with Maclurea, Trenton and Hudson with Ambony- 
chia radiata, C'yrtolites ornatus, Medina with Pleurotomaria 
litorea, Corniferous with Conocardium trigonale, Atrypa 
reticularis, Favosites polymorpha, Hamilton with Spirifer 
mucronatus, etc. 
The granite boulders are ohen of large size, sometimes 
six feet and more in diameter, and flenerally rounded. 
The largest transported blocks I have seen are the more 
or less angular masses of corniferous limestone mentioned 
ona preceding page. 
Along the southern margin of the Drift area, especially on 
the slopes of the highlands of Northern Ohio, the Drift 
sands and gravels are of considerable thickness, forming 
hills of one hdd feet or more in height, generally strati- 
fied, but often without any visible irs, These de- 
posits are very unevenly distributed, with a rolling surface 
frequently forming local basins, which hold the little lakelets 
or sphagnous marshes so characteristie of the region referred 
