Periodical Literature. 323 



directly under the cultivated area; the soil at the margin is not 

 affected in the slightest. 



The soil cover has immense influence; a compact layer of humus 

 reducing soil moisture during the growing season. 



WassergeJialt diluvialer Waldhoden. Zeitschrift fur Forst und 

 Jagdwesen, Januar, 1906. Pp. 13-38. 



The palaeobotanist Potonie at Berlin, an- 

 Classification ticipating his great work on the origin of 



of coal, has published a brief resume regard- 



Humus Formations, ing the different forms and stages of humi- 

 fication. Humus, generally speaking, are 

 the solid (or dissolved) materials which remain as a result of the 

 decomposition of plants. This decomposition can proceed under 

 different conditions, the most important of which is presence or 

 absence of air. Accordingly, there are four varieties of decomposi- 

 tion, namely, mere destruction or decay (Verwesung), putrefaction 

 (Faulniss), and between these two lie muck formation (Ver- 

 moderung) and turf or peat formation (Vertorfung). 



The first process, destruction or decay, is a decomposition, in 

 which everything is turned into gaseous form, carbon oxide and 

 water, leaving no permanent, solid carbon products. 



Muck formation occurs with presence of insufficient oxygen, so 

 that a complete decomposition into water and gas cannot take place, 

 and a solid carbonaceous material, muck, remains. It is that which 

 we see in humid forests, and what makes the black soil in parks. 



When the supply of oxygen is still further reduced, turf forma- 

 tion takes place, tending towards muck. The peat bogs in which 

 this condition especially occurs exhibit plant growth in such a man- 

 ner that new generations continue to form on top of the decom- 

 posed and decomposing ancestors, so that continuously increased 

 exclusion of air takes place, which leads to the fourth process, 

 putrefaction, decomposition under total exclusion of air. 



In reality none of these processes occurs purely by itself, but 

 they proceed side by side, and interchange. In the two intermediate 

 processes of muck and turf formation an accumulation of carbonace- 

 ous matter takes place, the continuing decomposition leads to forma- 

 tion of coal. 



