30 MODERN RAVINES. [CHAP. XXL 



from 20 to 180 feet was the result. (See fig. 7, p. 29.) The 

 high road has been several times turned to avoid this cavity, the 

 enlargement of which is still proceeding, and the old line of road 

 may be seen to have held its course directly over what is now 

 the widest part of the ravine. In the perpendicular walls of this 

 great chasm appear beds of clay and sand, red, white, yellow, 

 and green, produced by the decomposition in situ of hornbleridic 

 gneiss, with layers and veins of quartz, as before-mentioned, and 

 of a rock consisting of quartz and felspar, which remain entire to 

 prove that the whole mass was once crystalline. 



In another place I saw a bridge thrown over a recently formed 

 gulley, and here, as in Alabama, the new system of valleys and 

 of drainage, attendant on the clearing away of the woods, is a 

 source of serious inconvenience and loss. 



I infer, from the rapidity of the denudation caused here by 

 running water, after the clearing or removal of wood, that this 

 country has been always covered with a dense forest, from the 

 remote time when it first emerged from the sea. However long 

 may have been the period of upheaval required to raise the ma 

 rine tertiary strata to the height of more than 600 feet, we rnay 

 conclude that the surface has been protected by more than a mere 

 covering of herbage from the effects of the sudden flowing off of 

 the rain water. 



I know it may be contended that, when the granite and gneiss 

 first rose as islands out of the sea, they may have consisted en 

 tirely of hard rock, which resisted denudation, and therefore that 

 we can only affirm that the forest has been continuous from the 

 time of the decomposition and softening of the upper portion of 

 these rocks. But I may reply, that similar effects are observable, 

 even on a grander scale, in recently excavated ravines seventy or 

 eighty feet deep, in some newly cleared parts of the tertiary re 

 gions of Alabama, as in Clarke County, for example, and also in 

 some of the cretaceous strata of loose gravel, sand, and clay, in 

 the same state at Tuscaloosa. These are at a much greater 

 height above the sea, and must, from the first, have been as de 

 structible as they are now. 



We returned to Macon by our former route, through the pine 



