330 Adventures in Scenery 



has accumulated in the soil layers near the surface. Subsoils 

 have compacted, thereby giving water-holding quality, but 

 soils from all kinds of rocks do not behave in the same manner. 

 A "granite" soil is one thing; a limestone soil is another; a sand- 

 stone soil is different again; and a shale becomes a soil differing 

 from all the others. 



Granite Rock Breaks up into Clay 

 and Sand 



Granite rock, generally speaking, is composed of quartz, 

 feldspar and mica. Granite is thought of as a hard and durable 

 rock. Under the action of weathering agencies the hardest 

 granite crumbles and decays. The mica decomposes and be- 

 comes clay; feldspar, hard when fresh, breaks down into blue 

 clay; quartz, the hardest and most resistant to any dissolving 

 influences of weathering, persists, and the tiny particles become 

 the common sand of the soils. Thus granite rock decomposes 

 into loam a mixture of sand and clay. Shale, which when 

 metamorphosed by heat and pressure is slate, decomposes under 

 the action of the weather (frost, air, heat and moisture) and 

 becomes clay. Sandstone, which is quartz grains cemented 

 together, becomes sand when the cementing material is dis- 

 solved. Limestone, which when pure is calcium carbonate 

 (CaCO 3 ), dissolves in percolating soil water, carbon dioxide 

 escapes as a gas, and the lime, being soluble in water, leaches 

 away. Lavas, as rhyolite and basalt, break up under the action 

 of sunshine and rain and become clay, with some quartz sand. 



All the various types of rocks break up wherever exposed 

 to the action of the elements, and intermingle as they are washed 

 down the slopes, and hence the many types of soils in the val- 

 leys. Humus, or decayed organic matter, gathers in the soils 

 in the process of time, and thus the great variety of soils is 

 formed, differing widely in fertility or productiveness accord- 

 ing to the varying conditions under which they form and the 

 variety of materials of which they are composed. Iron, an ele- 



