DISTRIBUTION OF RESIDUAL MATERIAL. 555 



of this material and its transportation, separation and deposition by the 

 epigene agents of erosion ought, perhaps, to be considered here; but this is 

 a subject so large and complicated that it is ordinarily given a separate 

 treatment in physiography; therefore no attempt will be here made even 

 to summarize this part of the cycle of the movements and alterations of the 

 material of rocks. The residual undissolved material of the belt of 

 weathering is a source of the mechanical sediments and the partial source of 

 the combined mechanical and organic or chemical sediments. 



This residual material is deficient in the elements which have been 

 taken in solution in large amounts; it is therefore complementary to the 

 dissolved material. It follows that the residual material which is the source 

 of the mechanical sediments is likely to be deficient, to a varying extent, 

 in the alkalies and the alkaline earths, and of these it is much more likely 

 to be deficient in sodium and calcium than in potassium and magnesium. 

 This is true without taking into account the mechanical -sorting. So far as 

 there is mechanical sorting, there may be deficiencies or excesses of other 

 elements. But it may here be suggested that the deficiency in certain 

 elements, as compared with the original rocks, furnishes an adequate 

 reason why the mechanical sediments, when metamorphosed, do not 

 reproduce mineral combinations like those of the original rocks. The 

 metamorphosed equivalents of the mechanical sediments will naturally be 

 deficient in minerals rich in sodium and in calcium, such as sodalite, 

 nephelite, anorthite, etc. 



RELATIONS OF BELT OF WEATHERING TO SEDIMENTART ROCKS. 



BELT OF WEATHERING THE SOURCE OF SEDIMENTARY ROCKS. 



The materials transported to the sea in suspension and in solution by 

 overground and underground waters, and subordinately by the wind and 

 ice, supply the materials for the sedimentary rocks. These materials are 

 almost wholly derived, directly or indirectly, from the belt of weathering. 

 The main source of the sedimentary rocks is therefore the belt of weathering. 

 The material derived from the belt of weathering is transported in suspension 

 and in solution. 



