436 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



some writers improperly termed gneiss. The mass exhibits oc- 

 casionally a distinct cross-stratification, and pieces of compact 

 kaolin, sometimes angular, are imbedded in it. In other places, 

 as at Somerville, red, vermilion-coloured, and white clays, 180 

 feet thick, are seen. These rest in horizontal beds on the edges of 

 highly inclined strata of chlorite schist and clay-slate, which are ex- 

 posed to view at the rapids of the Savannah River, three miles above 

 Augusta. On Ray's Creek, near this point, the old schists, much 

 charged with iron, are seen to decompose into materials so like 

 the red vermilion- coloured clays of the tertiary deposits, that they 

 would be undistinguishable, were it not that the veins of quartz, 

 which have not decomposed, still remain running through them. 

 The quartz itself, when broken up, would furnish a white sand 

 such as that found associated with the red clays, so that we have 

 here a most satisfactory explanation of the derivative origin of a 

 great part of the burrstone formation. 



Savannah River. — I shall now describe several natural sections 

 which are seen in the bluffs or cliffs bounding the alluvial plain of 

 the Savannah River, in its course of about 250 miles between 

 Augusta and the sea. The river has an average fall of about one 

 foot per mile, or 250 feet between Augusta and the delta of the 

 river. Like the Mississippi and all large rivers, which, in the 

 flood season, are densely charged with sediment, the Savannah 

 has its immediate banks higher than the plain intervening be- 

 tween them and the high grounds, which usually, at whatever 

 distance from the river, present a steep cliff or " bluff" towards it. 



Near Augusta, the Savannah cuts through the red clays and 

 sands before mentioned. Forty miles below the city, a section 

 from 120 to 150 feet high, and half a mile in extent, is observed 

 in Shell Bluff in Georgia, on the right bank. Unfortunately, at 

 the time of my visit the waters were high, and covered the bottom 

 of the bluff. The lowest exposed portion of the cliff consisted of 

 white pulverulent marl, derived chiefly from comminuted shells, 

 which passed upwards into a solid limestone, sometimes concre- 

 tionary, and containing numerous casts of shells ; and above this 

 was again seen pulverulent white marl. Still higher, the calca- 

 reous deposit becomes more sandy and clayey, and encloses a bed 

 of huge oysters ( 0. Georgiana Conrad), which are found growing 

 one upon the other, and have evidently not been drifted into their 

 present place. The total thickness of these calcareous strata is 

 about 80 feet, above which, beds of red loam and yellow sand, such 

 as prevail at Aikin and Augusta before mentioned, and without 

 fossils, are seen at the top of the cliff 40 feet or more in thickness. 



After a diligent search of several days, I obtained casts of no 

 less than thirty-nine species of shells from the limestone of Shell 

 Bluff, twenty-four of which I have been able to identify either with 

 eocene species, known to Mr. Conrad to occur at Claiborne, or to 

 species found by me in other eocene localities, and I have no doubt 

 that I could have identified more had my own collection from 

 Claiborne been more complete. 



