SOILS — FERTILIZERS. 515 



of the hard ortsteiu, wbicb not only decreases the effective depth but also the 

 food supply. 



Three types of soil inclined to swamp formation were found In the colored 

 sandstone regions: (1) White soils (Molkenbuden), the weathering product of 

 hard sandstone; (2) red clay, the weathering product of soft stone; and (3) 

 red clay, underlying white soil. The white soils consist of a bleached out sur- 

 face layer and an impervious substratum. Their characteristic property is a 

 high content of dust and fine matter, and their main difference from the red 

 clay is a lower total clay content but a higher silicate content. Drainage, 

 forestation, mechanical cultivation, and liming are suggested for the improve- 

 ment of white soils. 



Polygon soils and " thuf ur " on Iceland, T. Tiioroddsen (Mitt. Justus 

 Perthes' Qeogr. Anst., 59 {1913), N-ov., pp. 253-255). — The author reports the 

 apparently widespread formation of the so-called polygon and " thufur " or 

 hilly soils, which, he thinks stand in close genetic relation, in that variable 

 evaporation, freezing, thawing, and the absence of drainage are essential condi- 

 tions for the formation of both. 



The polygon soils are said to occur only in flat soils of mixed clay and tufa, 

 being divided into more or less regular polygons of wet clay, 1 to li meters in 

 diameter, which are separated by frost cracks filled with small stones, tufa, 

 and refuse. Freezing is thought to force the coarse material down and later- 

 ally, while thawing, capillarity, and evaporation bring the fine material to 

 the top. 



The hilly or thufur soils are described as little knolls from * to 2 meters 

 in diameter, and from i to ^ meter high. The upper layer consists of 

 humus and plant residue, and the interior of mixed soil and clay. These 

 knolls are also separated by frost cracks and are thought to be formed in 

 the same manner as the polygon soils, except that the rise of fine matter is 

 more rapid. 



Problems in the study of forest soils, G. A. R. Borghesani {Gdor. Geol. 

 Prat., 11 {1913), No. 3-4, pp. 215-222, pi. i).— The author emphasizes the im- 

 portance in forest culture of choosing kinds of trees best adapted to the chem- 

 ical properties of a particular soil, and of fertilization adapted to the kinds of 

 trees chosen. Attention is further drawn to the effect of the litter covering on 

 the conservation of forest soils. 



The gases of swamp rice soils, W. H. Harrison and P. A. Subramania 

 AiYER {Mem. Dept. Agr. India, Chem. Ser., 3 {1913), No. 3, pp. 65-106, pis. 7, 

 jfig. 1; ahs. in Jour. Soc. Chem. Indus., 32 {1913), No. 24, p. 1165; Nature 

 ILondoji], 92 {1914), No. 2307, p. 564; Chem. Ads., 8 {1914), No. 4, p. 772).— 

 Investigations of the gases in swamp rice soils to determine their composition 

 and relation to manuring and crop growth led to the following conclusions: 



The normal fermentation of green manure in swamp paddy soils produces a 

 relatively large proportion of methane, a smaller amount of nitrogen, and some 

 carbon dioxid and hydrogen. The introduction of a crop so modifies the gas 

 production as to reduce the proportions of methane and hydrogen and increase 

 that of nitrogen. The restrictive action of crop growth on methane and hydro- 

 gen formation is due to retardation of fermentation or to absorption of a por- 

 tion of the intermediate products of decomposition by the roots. The retarda- 

 tion of the normal evolution of nitrogen by crop growth indicates that there 

 is an unknown surface evolution of nitrogen not connected with soil fermenta- 

 tion or the surface film which is affected by crop growth. 



An anaerobic condition prevailed in the soil immediately after irrigation and 

 throughout the irrigation period, making nitrification impossible and causing 



