io6 GEOLOGICAL SURVEY OF NEW JERSEY. 



experiments that a forest soil with a good layer of humus will 

 lose two and one-half times less water by evaporation than forest 

 soil where the humus is wanting. 



Humus, by mingling intimately with the mineral soil, adds to 

 it a proper consistency ; it makes binding soils more porous, and 

 loose soils more tenacious. It moderates the extremes of tem- 

 perature in the soil, and this is of great importance in sandy 

 regions. Not only does humus possess the power of absorbing 

 water, vapor and heat, but it has the ability to absorb some of 

 the most important food materials of plants as well. Thus 

 nitrates, phosphates, ammonia, &c., are held in solution ready 

 for the use of the plants. Without humus many of the most 

 important mineral materials would be washed away, especially 

 from the loose soil of South Jersey. 



Humus acts further as a reservoir from which food materials 

 may be obtained, and by means of which they may be made 

 ready for the use of the tree in growth. The final products of 

 the decomposition of the humus are the mineral ashes, carbonic 

 acid gas, and water. Through the ashes of the leaves, twigs, 

 etc., a large amount of the most important materials used in the 

 manufacture of wood are returned to the soil, and that in the 

 most usable form. The carbonic acid gas acts powerfully toward 

 the disintegration of the soil and in making the food constitu- 

 ents soluble, and in many sandy soils the value of its presence is 

 very great. Thus the humus is really a manure to the forest. 



If this layer of vegetable mold is destroyed the soil is impover- 

 ished at once. It loses one of the most powerful agents in its 

 decomposition, loses its activity also, and finally becomes prac- 

 tically dead. In Europe it has been long recognized that the 

 presence of humus is very beneficial to the forest, and. its absence 

 disastrous. This has led to laws forbidding the removal of the 

 litter by peasants. The experience of the Germans has taught 

 them that when the litter is continually taken away the forest 

 becomes more and more open, the sun's rays and a freer circula- 

 tion of air are admitted, the humus disappears, the soil dries out 

 and the trees become short, scrubby, and short-lived. Further, 

 the soil eventually becomes so impoverished that trees which 

 were at first produced are replaced by less fastidious and usually 

 less valuable species. Thus in many parts of Germany, where 



