FUNDAMENTAL PROBLEMS OF GEOLOGY. 245 



leaching process is this : Through the action of the atmosphere and 

 atmospheric waters the basic material is more largely dissolved and 

 carried awa}- than the acidic. When the weathering is thorough, 

 the residue is chiefly quartzose sand — if the original rock contained 

 quartz — and various residual earths and clays which are essentially 

 silicious silts and aluminum silicates, with a low percentage of the 

 basic oxides. If these earths and clays are turned back into cr3's- 

 talline rocks by metamorphism, the)' form acidic schists or gneisses, 

 while the quartzose sand becomes quartzite. The material borne away 

 in solution consists mainly of compounds of the alkalies and alkaline 

 earths. A part of this is redeposited -within the zone of the hj^dro- 

 sphere beneath the land, and a part is borne to the sea and remains in 

 solution or is deposited beneath it. Although some decomposition 

 takes place in the zone of the hydrosphere beneath the land, and some 

 also beneath the permanent water bodies, it is clearly less than that 

 which takes place in the zone of the atmosphere, and this difference 

 in the sum total of work done is all that need here be considered. 

 There can be no question that the land areas lose by leaching and 

 the water areas gain correspondingly. The general effect is an in- 

 crease in the acidity and a reduction in the specific gravity of the 

 land material. This includes the land wash deposited on the borders 

 of the continents. 



Now, when the growing hydrosphere crept up to the surface and 

 covered the lower tracts a selective action of this kind began. The 

 surface material of the areas that remained exposed lost more of its 

 basic than of its acidic constituents, while the submerged material 

 lost less and perhaps gained something by the redisposition of the 

 matter borne in from the land. As the planetesimals were being 

 gathered in on land and water alike, those that fell on the land suf- 

 fered some atmospheric action, while those that fell into the water 

 were mainly protected from it. As this differential action affected 

 each successive layer of growth after the accumulation of surface 

 waters began, the specific gravity of the land areas came to be less 

 than that of the submerged areas. 



It is not the temporary specific gravity that resulted from the 

 change of ph3'sical state involved in disintegration that is to be con- 

 sidered here, but rather what may be termed the inherent or perma- 

 nent specific gravity — /. e. , the specific gravity that would be retained 

 after any metamorphism which the material might probably suffer 

 in the future had taken place. So, likewise, it is not the temporary' 

 chemical combinations arising immediately from the weathering, but 



