188 Correspondence — A. R. Hunt. 



In the neighbourhood of Aldwarke and Thvybergh extensive 

 workings have proved that wash-outs have occurred at various 

 horizons in the Middle and Lower Coal-measures, and the limits of 

 certain of these have been accurately laid down on plans. 



Denudation in the Barnsley Seam has been found over an area 

 1.700 yards in length from east to west, and in the Parkgate Seam 

 (240 yards below) over an area 2,600 yards long from north to 

 south. In neither case was the wash-out completely crossed, but 

 its width cannot be less than 600 yards. The Swallow-Wood Seam, 

 lying 60 yards below the Barnsley and above the Parkgate Seam, 

 has been partly worked under the same area ; but no signs of 

 a wash-out have been found. 



The opinion of the author is that the wash-outs occupy the sites of 

 winding streams, meandering through the alluvial tracts in which 

 the coal-seams were beino- formed. 



Go:Eai2,Eisi^oiTnD.Bisrc:E!. 



FIVE THEORIES OF THE DEVON SCHISTS. 

 Sir, — Your reviewer has perhaps been unduly, and doubtless 

 unintentionally, severe on the whole army of martyrs who have 

 sacrificed themselves on the altar of the Devonshire schists during 

 the past sixty-eight years. He hopes that mere hypothesis will 

 «()on give way to a more reasonable and probable interpretation of 

 tJie facts. But, in truth, there has been but little hypothesis ; though 

 v\ e undoubtedly have several elaborate theories, based on evidence 

 much of which has seemed to eminent men worth consideration. We 

 have had, for instance, the following distinct lines of argument : — 



1. The schists are Upper Devonian, based on a certain interpre- 

 tation of the anticline at Mudstone Bay, near Berry Head, and other 

 stratigraphical facts. 



2. The schists are Archaean, based on elaborate microscopical 

 observations backed by great experience. 



3. The schists are Devonian, based on a comparison of the slates, 

 sandstones, and volcanic rocks between Scabbacombe Sands and 

 Stoke Fleming with the schists between Hall Sands and the Prawle 

 Point. 



4. The Start schists are Lower Devonian, based on a comparison 

 of the microscopical composition, character, and fineness of grain of 

 the quartz-schists with those of the Lower Devonian thin-bedded 

 sandstones. 



5. The schists are older than Devonian, but not necessarily 

 Archaean. The positive arguments in favour of this view I do not 

 fully grasp. 



Curiously enough, the authors of the Memoir, in their list of 

 literature, have missed a most important paper, viz. "The Meta- 

 morphosis of the Rocks extending from Hope Cove to Start Bay," 

 by W. Pengelly, F.R.S. (Trans. Dev. Assoc, 1879). This paper is 

 very important as a summary of the current opinions then held by 

 geologists. The Upper Devonian age of the schists was treated as 



