686 GEOLOGY OF OHIO. 
ous travertine, which is deposited as an incrustation on pebbles, bowlders, 
shells, and vegetable growths. But since the drainage courses have all 
been opened out, a few hours’ rain is often sufficient to produce a flood 
which easily sweeps away the light and porous travertine, to re-deposit 
it at lower points along the courses of the stream. It must also be added 
that the carbonate of lime in the soil is partly due to land shells which 
have lived and died upon its surface. 
2. The soils formed from the high-level gravels are very closely allied 
in origin and character to those found on the gravel terraces or second 
bottoms of the rivers. They are not, however, underlain by as porous a 
subsoil as the latter, and therefore prove, as a rule, more retentive and 
durable. They are scattered through the highlands of the county in iso- 
lated patches, often of small extent. They are as plainly recognized be- 
fore the country is cleared as after the soil has been exposed by the plow, 
for the natural growth of forest trees which they produce distinguishes 
them unmistakably from the colder lands adjoining and surrounding 
them. On the gravel points are found the black walnut, the sugar tree, 
the blue ash, the hickory, etc., while the clay lands show little but oaks. 
In color they are reddish-brown, verging towards black in many cases. 
Under cultivation they are extremely productive, and always constitute 
the favorite portions for tillage of every farm on which they occur. 
An analyses of one of these gravel point soils is given below (No. 4). 
The specimen submitted was taken from the farm of John Howell, Esq., 
in Mad River township, a few miles north of the Greene county line. It 
will be seen that the testimony of chemistry fully accords with that of 
experience with reference to these soils. Like analysis No. 8, this soil 
might almost be assumed as a model. Its seventy per cent. of silica, 
mixed with nine per cent. of alumina, render it certain that it will work 
light, especially when its nine per cent. of organic matter is taken into 
account. It contains over three and one-half per cent. of the alkalies, soda, 
and potash, while the supply of phosphoric acid is ample for generous har- 
vests. Though derived from the decomposition of limestone pebbles very 
- largely, but little lime remains in its composition (less than four per cent. 
of lime and magnesia). This fact seemssurprising at the first statement, 
but a little reflection shows us that it is a necessary consequence of the 
mode of formation above described. The pebble that is to be turned into 
soil consists of carbonates of lime and magnesia in large proportion, and 
of sand, clay, iron, etc.,in much smaller proportions. But these latter 
substances are all that are turned over to the forming soil, and they are 
set free only by the solution and removal of the lime and magnesia. The 
percentage given above is more than sufficient, however, for the demands 
of vegetation. 
