Vol. 65.] AROUND PLYNLIMON AND PONT EEWIB. 537 



District type, rather than of the Rhayader type, while at Plynlimon 

 the change had already begun. It had been left to the Author to 

 prove conclusively the geological structure of this tantalizing region 

 and to place its classic strata in their correct order. With the 

 Author's careful and detailed work here, and with the far-reaching 

 discoveries of Mrs. Shakespear at Tarannon, it might be truly 

 said that the mystery of the vast Mid-Wales complex was solved 

 at last. It seemed probable that the remaining area would prove 

 to be made up of mere variations of the Plynlimon-Tarannon 

 geology : in other words, great stretches of Tarannon rocks, with 

 small patches of Llandovery and Hartfell brought up in anticlinal 

 folds. 



The President (Prof. Sollas) remarked on the interesting manner 

 in which the uniform colour of the ' Welsh wilderness ' had been 

 transformed into a diversified scheme of stratigraphical structure. 

 The constancy of lithological character on some horizons was 

 a very suggestive fact, and under the guidance of palseontological 

 evidence might lead to unexpected discoveries concerning the 

 geographical features and physical conditions of past ages. The 

 Monograptus priodon limestone retained its black colour and thin 

 slabby bedding over a wide area ; examples from Bohemia and 

 Ireland were undistinguishable in hand-specimens, and were re- 

 markably similar to others from Cincinnati in Ohio. 



The Author, replying to Dr. Marr, said that one of the specimens 

 exhibited on the table was a pale greyish-green flag about three- 

 quarters of an inch thick, which occurred throughout the Pont 

 Erwyd district in the centre of the leptotheca band. This band 

 might be correlated with certainty with the argenteus zone of the 

 Lake District, and the pale flag in the centre was almost certainly 

 equivalent to the peculiar ' green streak ' which had been found 

 over a wide area in the Lake District, always at the centre of the 

 argenteus shale-band. Dr. Herbert Lapworth had referred to the 

 peculiar structure in the mudstonesof the Plynlimon Stage as a double 

 cleavage, and seemed to suggest that it required two series of move- 

 ments to set it up. The Author was of opinion that it was the 

 effect of a single set of movements on sediments of a certain physical 

 constitution. In conclusion, the Author thanked the Pellows 

 present for their cordial reception of his paper. 



