10 The American Geologist. January, 1895 
bly from neighboring bluffs. This local material is sometimes 
angular, but more generally is semi-rounded. Pebbles several 
inches in diameter have been found, and these are sharply 
angular. There also occurs among the gravel a great variety 
of drift pebbles. The sand is composed chiefly of well rounded 
grains of transparent colorless quartz. At one locality a 
gravelly stratum near the top of the deposit was lithified, by 
reddish brown oxide of iron, into a soft conglomerate. In the 
valley of Crane's creek a considerable portion of the gravel 
consists of fossiliferous limestone of ('incinnati age, which 
could not have been derived from the drift in the immediate 
vicinity but must have been brought by strong currents of 
water from the outcrop of the Cincinnati strata, several miles 
up the valley. 
The composition, structure, and limited distribution of this 
njember of the Columbia formation show it to be a river de- 
posit, such as is laid down by streams of a moderate gradient 
at the present day. Its surface maintains a nearly constant 
level relative to the present water level, presumably indicat- 
ing the flood-plain level of the Florence streams. This opin- 
ion is further supported by local patches, apparently similar 
to the alluvial soil at the surface of our present flood-plains. 
Now, accepting the hypothesis that the surface of the deposit 
represents the ancient flood-plain level, we find that this level 
averages 10 feet or more below the alluvial plains of the pres- 
ent streams. It is generally conceded that the absolute ele- 
vation of a flood-plain in any given region is directly de- 
pendent on the relative altitude of the land above sea level, 
the flood-plain rising if the land is depressed, and, vice versa, 
disappearing and forming at lower levels or ceasing to be a 
flood-plain if the land is in process of elevation. As there is 
no evidence supporting the supposition that the relation be- 
tween altitude and water level was materially different, dur- 
ing the period of the growth of the Florence flood-plain, from 
what it is at the present day, we may safely assert that the 
land then stood at a slirfhfli/ higher altitude than it does at 
present. 
This land was also then in process of depression. The Flor- 
ence flood-plain passes through the old interglacial rock 
gorges, which are quite numerous in the Pecatonica basin, and 
