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. 3, 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 seems surprising 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. 



