PAET V 



THE EBGOLITH 



Throughout all the the millions of years which have elapsed 

 since the earth assumed its present form and essentially solid 

 condition, the rocks composing its more superficial portions have 

 been constantly undergoing degeneration in the manner de- 

 scribed, and, in so doing, have given rise to the immense masses 

 of materials which constitute the thousands of feet of secon- 

 dary rocks and the still unconsolidated sands, gravels, and other 

 products which will be considered in detail later. "With those 

 products which have undergone lithification, which are now in 

 the state of consolidation commonly ascribed to rocks by the 

 popular mind, we shall have little more to do. These have 

 already been sufficiently described as rocks in Part II of this 

 work. It is to the most superficial and unconsolidated portion 

 of the earth's crust that we will now devote our attention. 



Let the reader for a moment picture to himself the present 

 condition of this crust, with particular reference to the land 

 areas. Everywhere, with the exception of the comparatively 

 limited portions laid bare by ice or stream erosion, or on the 

 steepest mountain slopes, the underlying rocks are covered by 

 an incoherent mass of varying thickness composed of materials 

 essentially the same as those which make up the rocks them- 

 selves, but in greatly varying conditions of mechanical aggrega- 

 tion and chemical combination. 



In places this covering is made up of material originating 

 through rock-weathering or plant growth in situ. In other 

 instances it is of fragnuental and more or less decomposed mat- 

 ter drifted by wind, water, or ice from other sources. This 

 entire mantle of unconsolidated material, whatever its nature 

 or origin, it is proposed to call the regolith, from the Greek 

 words /^i^T-oc, meaning a blanket, and liOoq, a stone} Within 

 certain limits it varies widely in composition and physical proper- 



^ From a strict pMlological standpoint tlie word, it will be noted, should 

 have been spelled rhegoUth, 



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