290 THE EEGOLITH 



The prevailing characteristic of an old residual deposit, from 

 whatever rock it may be derived, is a ferruginous clay. Exam- 

 ined by a microscope, its mineral particles, when not too thor- 

 oughly decomposed, are found to be sharply angular in outline. 

 With the exception of the quartz, the various mineral constitu- 

 ents are often in an advanced stage of decay, and the more 

 soluble constituents are wholly or partially lacking, having been 

 leached out, in the manner already described. (See under Soil, 

 p. 345.) 



The colors are dull, or some shade of brown or red, owing to 

 the higher oxidation and perhaps dehydration of the ferruginous 

 matter set free by the decomposition of the iron-bearing sili- 

 cates. Such in general are the residual soils of the southern 

 Appalachian regions of the United States which are apparently 

 comparable with the terra rossa of Europe, but only in a slight 

 degree with the laterite of India, to which they have often un- 

 fortunately been referred.^ From a chemical standpoint the 

 soils forming the upper portion of the residuary deposits vary 

 widely from the rock masses from whence they were derived, 

 much depending upon their age and the amount of actual de- 

 composition and leaching that has taken place. On p. 347 are 

 given a few typical but widely varying analyses which will serve 

 to illustrate this point. 



Deposits of this nature are never truly stratified, excepting 

 where, through having remained wholly undisturbed, they re- 

 tain the original structure of the parent rock. (See under 

 Effacement of Original Characteristics, p. 249.) 



The residuary differ from the drift deposits in that they con- 

 tain no materials foreign to their vicinity, but only such more 

 enduring matter as has been handed down to them from the 

 parent rock. In the ease of limestones such matter consists 

 mainly of aluminous and ferruginous matter, grains of sand, 



^ The term terra rossa, accordiDg to Neumayer (Erdgeschichte, Vol. I, p. 

 405) was first applied to the red residual deposits in the Karst maritime 

 lands of the Adriatic Sea. The material is described as a highly f erruginoua 

 clay resulting from the leaching out, by meteoric waters, of the soluble 

 portions of the prevailing limestones. Its distribution is by no means limited 

 to the maritime provinces of the Karst, but it is found also on the Grecian 

 coasts and in the Schwabia-Fxankonia Jura Plateaus of Bavaria. In fact 

 it is to be found anywhere in regions where the prevailing country rock is 

 a marine lim'estone and erosion not sufficiently active to remove the residu- 

 ary material. 



