710 EXPERIMENT STATION RECORD. 



of Europe, Asia, America, Africa, and Australia, /. r., in the second, 

 third, and part of the fourth zones. {'2) Humus-calcareous soils. 

 Hunuis-containing soils are formed from calcareous rocks (limestone, 

 marble, chalk, etc.) accunudating nuich humus in consequence of the 

 rapid leaching out of the calcium and magnesian carbonates and the 

 retarded decomposition of the organic remains in the feebly alkaline 

 medium. (3) Marsh}" soils. Under this term are understood soils 

 which owe their origin to the influence of stagnant waters (water- 

 logged soils) dispersed over the surface of continents, wherever the 

 relief and the hydro-geological conditions favor their formation. They 

 occur most frequently in temperate and frigid zones, although some- 

 times found in the arid zone. They are formed (a) in a medium of 

 fresh water (sour meadows, the marshes of the lowlands), or (b) in sec- 

 tions which are or have been subject to inundations by the sea or by 

 the waters of estuaries (sea marshes, salt marshes, delta marshes, etc.). 

 The different stages in the formation of the swamps, the diverse com- 

 position of the organisms, the character of the aqueous medium, the 

 drying up of the marshy basin due to various causes, give to the soils 

 of this type a great variet)\ 



Lastlv, there are many natural soils which are composed of the 

 unaltered parent rock (when forming in .s!fi() to the almost complete 

 exclusion of line earth and humus, or which are formed l)y a mixed 

 process (1) by the mechanical deposition of particles, mineral as well 

 as organic (alluvium); and (2) by the periodic action on the alluvial 

 deposits of the special factors which form humus soils. The soils of 

 this nature stand, so to speak, on the border line between soils proper 

 and rocks, in one case merging into soils, in another approaching rocks. 

 They form the third class of incomplete or azonal soils; they are met 

 with everywhere. When they are formed in situ, outside of alluvial 

 depressions and valleys, the}^ can be divided into two large groups, 

 (1) crude soils and (2) skeleton soils. By crude soils are meant those 

 in which there is a considerable quantity of cla3^-like particles (clays, 

 silt, and fine sand), but in which the horizon of vegetable humus is 

 not clearly defined. Every humus soil passes downward into a crude 

 soil, but the term is applied here only to those soils which are wholly 

 or almost wholly crude. The name skeleton soil is applied to those in 

 which granular and sandy, gravelly, or pebbly elements, or in general, 

 the skeleton mechanical elements which take the place of the humus 

 and fine earth, entirely predominate. 



Among the conditions which conduce to the formation of crude and 

 skeleton soils are the following: 



(1) Unalterability or difficult alterability of the parent rock or of 

 the rocky components of the soil (sand, rock fragments, pebbles, com- 

 pact sedimentary rocks, etc.). 



