Dec., 1908 .] 
Rock Terraces. 
403 
far cut into the rock that its valley shall be ornamented with 
terraces as are its larger neighbors. Its problem will then, 
however, be somewhat complicated, if its alluvial terraces shall 
persist that long, for today the Big Darby has many fine terraces 
of this more ephemeral type. 
In conclusion, a few facts and deductions may be noted. 
1. The grade of the rivers has been reduced since the 
terraces were made. Almost every terrace top is nearer the 
river level at its downstream end than at the other. And 
further, an analysis of the slopes of the various terrace tops 
shows that the higher ones descend downstream most rapidlv, 
and the lower ones but little faster than the present water level. 
The average fall of the present Scioto across the quadrangle is 
(if feet per mile; that of the Olentangy is 5 1 '■> feet per mile -bee 
line distances. The upper terraces fall 20 feet per mile and some 
of the lower ones about 10 feet per mile. 
2. This relation just noted confirms a statement made 
earlier in the paper, that the terraces, with two possible excep¬ 
tions, were made by the present streams. The same statement 
is further confirmed in the fact that all terraces descend south¬ 
ward or with the present drainage. 
3. It has been pointed out that in harmony with the slight 
eastward dip of the rock and the customary streamward slope 
of the terrace tops, those on the west side are usually structural 
plains, while those on the east side are usually not. 
4. The terraces are confined to country whose surface rock 
is limestone, or limestone with a very little shale cover. The 
shale alone seems not to be adapted to terrace formation. It 
might be added here that in one side stream good terraces were 
found consisting of Ohio shale from which the thick drift cover 
had been removed. The shale proving a much tougher material 
than the drift the stream has, to date, been unable to make 
nearlv as wide valley in it as was made while still cutting in the 
drift above. Hence is found a large shale terrace svmmetricallv 
disposed on each side. 
5. The terraces are of marked economic importance, offer¬ 
ing good roadways above flood waters, good building sites above 
the fertile flood plains but not so far away as sites on the uplands 
must needs be. Springs frequently occur at the back side of the 
terrace, making them still more desirable for residences. Finallv 
most of the quarries are in these terraces, because of the excel¬ 
lent opportunities to get at the rock. 
