100. 



Dolomite soils are in "bad repufe, in both the United States and 

 Europe. They are barren soils. MgO "becomes poisonous to plants unless 

 CaO is present. 



8) Gypsum: ( CaSG^J : does not occur extensively. In gypsum lands 

 it trices the form of a sand. GyjDsum is a good fertilizer for bad alkali 

 lands; it acts as a corrector of the alkalies. 



9) Iron oxides and hydrates: these substances are freed from 

 rocks "by decomposition. They give color to soils, and form an important 

 part of the soil by becoming colloid materials with large water capaci- 

 ties. Hut too much of these substances is not good; some salts of J?e ar 

 injurious. 



. Various rocks contributing to soil and the Value of their pro- 

 duct."" 



^^ Rocks: are of three classes: eruptive, sedimentary, and 

 :.nrr.orphic. Van Hise considers that sedimentary and metamorphic rocks 

 ire not different from ea.ch other except in degree. 

 a) :;edimuntary rocks: 



(1) Limestones *>.re frequent and of many varities. They 



may contain as much as ^'O/i of foreign materials. They occur everywhere, 

 all over the earth. Garble is considered as metamorphic rock. Limestones 

 are found in all stages of development, and in general it may be said 

 thp,t they nmke ood soils. There are some exceptions; limestone bluffs 

 are not good soils: the drainage is poor, the soils are washed. Water 

 runs off easily, and carves out underground runways and caves, with ver^ 

 rapid circulation. Limestone regions are apt to be poor in well and cis- 

 tern supply. 



In decomposition soil loses a large part of its lime and becomes 

 silt and clay. In non-glaciated country we may have: 



Indissoluble 



material Lime 



Soil 



Sub-soil ?1> 1. 



Limestone 11# 80.0; 



Limestone soils are apt to sometimes be too good for forest pur- 

 poses. In order to make 100$ of limestone soil it was necessary to dis- 

 solve upwards of ?00# of original rock. Leeching must occur simultan- 

 eously with '^oil formation. Lime leaches out of limestone when it dis- 

 integrates; this is an important process. 



(2) Sandstones:, conglomerates, etc., to quartzite: these are 

 composed of sands and gravels which originated from the eruptive rocks, 

 \?ere decomposed from these rocks, washed over and cemented into new 

 rocks. The cements varied vrom iron or pure silica to clay, and often 

 varied with the coarseness of the sand. Soluble materials leach out in- 

 to the soils, which is a good process for the soils. Sandstones vary in 

 hardness to f? Ise quartzita. Calc limestone makes a good soil. 



(3) ^ales, clays, slates: are hard, with a metamorphic ten- 

 dency. They are of the same composition as granites, with 50-7t>/< 3i02 

 Their decomposition leads to a variety of soils. They vary in resis- 

 tance to decomposition, as some are very soft; they usually make stony 

 lands, and are very variable in quality from good fertile soils to poor 

 and extremely lean soils. Ordinary slate lands are good enough for hard- 



