70 Geological Society. 



Middle Devonian species in other areas ; and the three remaining 

 are either doubtful species or ones which have a great vertical range. 

 These facts show that the so-called Upper Devonian Rocks in this 

 area do not contain a distinguishing fauna of any importance j and 

 the stratigraphieal evidence is opposed to the view that they are a 

 series of rocks distinct from those on the north side of the Morte 

 Slates, which have been classed as Middle and Lower Devonian. 



December 10. — Dr. A. Geikie, F.R.S., President, in the Chair. 

 The following communications were read : — 



1. "On some Water-worn and Pebble-worn Stones taken from 

 the Apron of the Severn Commissioners' Weir erected across the 

 River at Holt Eleet about 8 miles above Worcester." By Henry 

 John Marten, Esq., M.Inst.C.E., P.G.S., &c, Engineer to the Severn 

 Commissioners. 



The Weir referred to in the paper was built in 1844 of soft red 

 sandstone, and some of the stones composing the apron of the Weir 

 showing signs of decay were removed in 1887. The average quan- 

 tity of water passing over each square foot of the stones composing 

 the apron has been estimated at about 2000 gallons per minute. A 

 large proportion of the stones had been drilled through and through 

 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 apron, 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., P.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 

 Appalachian 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 Yalley by a curved escarpment ; a similar though more in- 

 dented escarpment forming its north-western margin, and separating 



