Geological Society of London. 45 



large proportion of the stones had been drilled tbi-ough and throngli 

 by the action of the current upon small pebbles lodged in hollows or 

 between the joints of the stone ; and the author estimates that as a 

 result of 43 years of erosion, six of the stones of the api'on, which 

 may be taken as a sample, had lost the following amounts respec- 

 tively :— 45, 60, 48, 50, 37, and 58 per cent. 



2. " On the Physical Geology of Tennessee and adjoining Districts 

 in the United States of America," By Prof. Edward Hull, M.A., 

 LL.D., F.R.S., F.G.S., late Director of the Geological Survey of 

 Ireland. 



The area described in the paper is occupied by the Unaka or Blue 

 Ridge, which may be regarded as one of the parallel ridges of the 

 Alleghanies, and the prolongation of Prof. J. D. Dana's " Archaean 

 Protaxis." It runs in a general south-westerly direction, and attains 

 an elevation of 6760 feet. At its base, and to the north-west of it, 

 is the Valley of East Tennessee, about 40 miles wide, and furrowed 

 by north-east and south-west ridges and depressions, parallel to the 

 strike of the Cambrian and Silurian beds. Through this runs the 

 Tennessee River, which, instead of running south to the Gulf of 

 Mexico, turns to the north-west, some distance below Chattanooga, 

 and cuts through the Cumberland table-land, a prolongation of the 

 Appalacluan mountains, and flows into the Ohio River. 



The Cumberland table-land has an average height of 2000 feet 

 above the sea, and 1350 feet above the Tennessee River at Chatta- 

 nooga. It consists of a synclinal of Carboniferous rocks resting 

 conformably upon the Devonian beds, and is bounded along the East 

 Tennessee Valley by a curved escarpment ; a similar though more in- 

 dented escarpment forming its north-western margin, and separating 

 it from the Silurian plain of Nashville. The table-land is about 40 

 miles wide, and is intersected by the valley of the Sequachee River, 

 running in a north-easterly direction along a subsidiary anticline 

 from near Jasper for a distance of sixty miles. 



From the base of the Cambrian beds, the whole Lower and Upper 

 Paleozoic formations succeed each other in apparently conformable 

 sequence, except at the junction of the Upper and Lower Silu- 

 rian series, where a probable discordance occurs. The prolonged 

 period of subsidence and deposition at length gave way to elevation ; 

 acting with the greatest effect along the Alleghanies. Under these 

 circumstances, denudation proceeded most rapidly along the tract 

 bordering the Protaxis, whilst the synclines were protected from 

 erosion to a greater degree ; and as the elevatory movement was 

 more rapid along the Unaka range, the flow of the streams was 

 generally westward. At a later period the Cumberland plateau 

 began to be formed by backward erosion of the strata in the 

 direction of the dip ; so that it owes its development to the erosion 

 of the Tennessee and Clinch Rivers on the one hand, and to the 

 Cumberland River on the other. Where the Tennessee River flows in 

 a north-westerly direction through the Cumberland plateau, the divide 

 between it and the Gulf of Mexico is only 280 feet above the river- 

 bed, whilst the table-land is 1400-1500 feet above. The author 



