CHAP. XXL] MODERN RAVINES. 23 



eight or ten inches long, is seen to retain its angles, 

 although converted into kaolin. Similar crystals, 

 almost as perfect, may be seen washed into the tertiary 

 strata south of the granitic region, where white 

 porcelain clays, quartzose, gravel, sand, and micaceous 

 loam are found, evidently derived from the waste of 

 decomposed crystalline rocks. I am not surprised, 

 therefore, that some geologists should have con 

 founded the ancient gneiss of this district, thus de 

 composed in situ, with the tertiary deposits. Their 

 close resemblance confirms me in the opinion, that 

 the arrangement of the gneiss and mica schist in beds 

 with subordinate layers, both horizontal and oblique, 

 was originally determined, in most cases at least, by 

 aqueous deposition, although often modified by sub 

 sequent crystalline action. 



The surprising depth of some of the modern 

 ravines, in the neighbourhood of Milledgeville, sug 

 gests matter of curious speculation. At the distance 

 of three miles and a half due west of the town, on the 

 direct road to Macon, on the farm of Pomona, is the 

 ravine represented in the annexed wood-cut (p. 25.). 

 Twenty years ago it had no existence ; but when the 

 trees of the forest were cut down, cracks three feet 

 deep were caused by the sun s heat in the clay ; and, 

 during the rains, a sudden rush of water through 

 these cracks, caused them to deepen at their lower ex 

 tremities, from whence the excavating power worked 

 backwards, till, in the course of twenty years, a 

 chasm, measuring no less than 55 feet in depth, 300 

 yards in length, and varying in width from 20 to 



