RELATIONS OF DISINTEGRATION AND DECOMPOSITION. 503 



position be stayed. But areas of very low relief are favorable to decom- 

 position of the narrow belt extending to and somewhat below the level of 

 ground water. This' is well illustrated by Florida. In that region the. 

 original refractory minerals have been decomposed and the soluble material 

 abstracted; and the relatively soluble minerals, such as the calcium car- 

 bonate of the limestones, have been wholly abstracted, leaving for a large 

 part of the region a mantle of insoluble residual material, corresponding in 

 composition almost perfectly with the ultimate products of weathering. 

 (See pp. 520-521.) 



In contrast with low regions are regions where the altitudes are great 

 and the slopes steep. Disintegration and transportation may go on so 

 rapidly as to give little opportunity for decomposition. 



Thus the most favorable conditions for most rapid but not complete 

 decomposition' are limited both by very low and b} T very high altitudes. 

 Therefore, the most favorable topographic conditions for rapid decompo- 

 sition are those of moderate relief. Excellent illustrative regions are 

 southeastern United States, Nicaragua, and large parts of Brazil. These 

 are all regions of moderate elevation and continuous moderate slopes. 



Regions of abundant plants and animals. Plentiful plant aild ailimal life is Veiy 



favorable to decomposition. Abundance of plants and animals is condi- 

 tioned by high humidity and high temperature. Regions of abundant life 

 are therefore the warm, moist regions of the Tropics and the sub-Tropics. 

 It is not too much to say that abundant animals and plants and their 

 by-products are the sources of most of the active compounds, which, 

 working through abundant water solutions favored by high temperature, 

 do the great work in the decomposition of the rocks. As already pointed 

 out, the process of carbonation, one of the chief reactions of the belt of 

 weathering, is largely conditioned on the carbonic acid concentrated by 

 the decomposition of plants and animals. 



While the work of life is fundamental in the decomposition of the 

 rocks, where life is too abundant this may stay the progress of weathering. 

 Abundant plant life gives a protective covering to the decomposed rocks, 

 which is effective in proportion to its luxuriance. The plant covering, 

 where very luxuriant, as in many parts of the warm regions, very greatly 

 retards, and may almost wholly stop, the mechanical work of disintegra- 

 tion and transportation. Therefore, under these conditions, in very humid 



