224 THE LOWER PALEOZOIC EOCES [vol. Ixxviii, 



paper lias not yet been completely "written. In it an attempt is made to co- 

 ordinate the eartii-moyements and to explain their relations one to the other, 

 both in place and in time. The present paper describes the results of some 

 of these movements ; the future paper casts its net "wider, and also attempts 

 to give reasons for the moTements. Those movements that are mentioned in 

 Dr. Wills's and my paper can be more clearly demonstrated in the larger area 

 examined. 



' If there is one point that requires emphasis at this stage it is this — that 

 the cleavage-planes induced by the Caledonian directional movements, in the 

 ground least disturbed by later faulting and torsional movement, dip invari- 

 ably north"wards. This points to a relatively greater north"ward movement in 

 depth than at the surface.' 



Mr. C. B. Wedd congratulated the Authors, with whom he had 

 himself long been associated in Xorth AYales, on theii' success 

 in unravelling a complex and difficult piece of stratigraphy, and in 

 producing a very fine map. Dr. Wills had referred to certain 

 joint work on the tectonic structure of a larger district, by his 

 colleague Mr. B. Smith and the present speaker, who regretted 

 that that work was. not yet ready for presentation to the Society. 



The Authors had been handicapped in their account of the 

 structure of the district by rekictance to use unpublished facts, 

 of which they had knowledge, in regard to neighbouring gi-ound 

 outside their area. For example, the Minera fault-belt was 

 essential to an understanding of the movements that had affected 

 the Llangollen basin. That fault-belt, lying a little farther east, 

 was a crescentic dislocation, extending with eastward convexity of 

 cmwe from the combined Llanelidan and Bryneglwi,'s Fault in the 

 north to the Llangollen Fault in the south. It showed how the 

 Llangollen Syncline, with the adjacent anticline north of it, had 

 been torn away from the eastern tract and slewed southwards by a 

 rotary movement to which the Authors had alluded. That faidt- 

 belt, proved by mining in the southern part of its course, where 

 such a movement should afford relief from pressure, consisted of a 

 ' horst '-like arrangement of opposite throws, individually large, 

 but with no appreciable net result in vertical displacement, the 

 main movement having been chiefly in a horizontal du-ection. 



The speaker had called Dr. Wills's attention to the significance 

 of an apparent displacement of the trough of the Llangollen 

 Syncline beneath the Carboniferous rocks by the agency of the 

 Aqueduct Fault, as shown by that Author's elaborate sections 

 across the valley. 



Prof. 0. T. JoxES congratulated the Authors on the completion 

 of an admirable piece of stratigraphical work in a region of great 

 difficulty. He enquired whether it was still believed tliat there is a 

 break in the succession between the Caradocian and the Ashgillian; 

 if not, he would be inclined to suggest, in view of the developments 

 farther south, that the Blaen-y-cwm Beds will probably be found 

 to belong to the Dicellograptus-comjjlanatus Zone or to the 

 JD.-ancejJs Zone — in other words, to the L^pper Hartfell Group. 



The correlation of the shelly and graptolitic facies of the Bala 

 was still far from satisfactory, and, in view of the undoubted 



