300 OHIO BIOLOGICAL SUEVEY 



same rocks cannot have differed, in the beginning at least, in any im- 

 portant respect on the two sides. The only obvious difference between 

 the two slopes is the condition of the surface of the ground. The west 

 slope is covered with a deep carpet of fallen leaves and leaf mold while 

 the opposite slope is swept bare of leaves by the wind so that there is 

 little or no humus formed and the ground is somewhat more exposed 

 to erosion from surface runoff. The soil of the west bank gives a neu- 

 tral or faintly acid reaction to litmus paper. That of the east bank, 

 on the other hand, gives a very strong and almost instantaneous red 

 reaction. This is remarkable in view of the abundance of organic 

 remains which must liberate various acids in course of humification 

 in the neutral soil while the opposite acid bank is free from any such 

 source of acidity. Repeated tests throughout the area have uniformally 

 shown that wherever the characteristic upland forest develops, there 

 the soil gives a strongly acid reaction to litmus paper. The soil of the 

 lowland forest, on the other hand, always gives a faintly acid or neutral 

 reaction to the same test. 



Although such conditions have often been ignored in American 

 ecological papers, they are clearly recognized in Europe. "Warming in 

 his "Ecology," for example, speaks of the importance of sour humus 

 again and again. On page 62 he describes conditions practically iden- 

 tical with those found in the Sugar Grove region as follows: "Raw 

 (sour) humus appears in forests, especially in places exposed to wind, 

 while ordinary humus, with its earthworms and other animals, reigns 

 in places sheltered from dessication; when ordinary humus in the 

 beech forest has given way to raw humus because of timber falls and 

 such like, then the beech, being no longer capable of regenerating, 

 disappears, and is often replaced by calluna heath." 



While the situation is more complicated in the case of cultivated 

 fields, it seems not unlikely tliat exposure is an important factor in 

 increasing their sterility just as with the forests. This prol^ability 

 together with the fact that exposure and danger from Avash in large 

 measure go band in hand would seem to lay down very clearly the 

 lines along which experimentation should proceed. 



The only practicable method of reducing exposure is, of course, 

 reforestation. Reforestation of ail washed slopes and of all in danger 

 of washing, would not only save the soil in many fields where it is cer- 

 tain to be washed off sooner or later, but would provide windbreaks 

 sufficient to protect the larger part of the more level upland fields. 



