136 MR. H. LAFWORTH OST THE [Feb. I9OO, 



The Bev. J. F. Blake said that he had listened with much interest 

 to the paper. The country described seemed to show special strati- 

 graphical features which had been admirably worked out by the 

 Author. When, however, one attempted to assimilate his conclusions 

 some questions arose. The limitation of the conglomerate was most 

 remarkable, and the Author's diagram indicated that he considered 

 this limitation original. There were no doubt, in Central Wales, 

 other limited patches of conglomerate, but their occurrence suggested 

 a question as to the systematic value of the unconformity. There 

 was a suspicious approximation to parallelism in the strata above 

 and below the line of unconformity, which reminded one of text- 

 book figures illustrative of ' contemporaneous erosion.' Iu this con- 

 nexion the speaker called tomindthe conclusions of the late Walter 

 Keeping, who distinctly asserted, and argued about, the absence of 

 any unconformity here. His explanation of the district was quite 

 different from that of the Author, and if he did not miss the un- 

 conformity he must have regarded it as being of no systematic value. 

 It was stated also that graptolites in the beds above and below both 

 belonged to the ' Biikhill ' Group, the only distinction being between 

 ' Upper' and ' Lower' ; and the speaker thought it unadvisable to 

 perpetuate the confusion arising from such nomenclature in the case 

 of the ' Llandovery,' which included an unconformity in its midst. 

 He also drew attention to some strange results to which we seemed 

 to be led by the guidance of the graptolites. Walter Keeping had 

 united two rocks, one at Aberystwyth and the other at the Devil's 

 Bridge, separated by apparent stratigraphy by nearly 4 miles in 

 thickness of rock, on the strength of their graptolitic fauna being the 

 same — really only 2 out of 8 species agreed, but these were considered 

 the most important ; and now we should have similar identifications 

 as far as Rhayader. It was really remarkable that so vast a sweep of 

 country and such enormous thicknesses actually observed in the hills 

 should be referred to one limited ' Birkhill ' or ' Llandovery ' horizon ; 

 and still more remarkable that, though Llandovery itself was almost 

 in sight, the correlation should have to be made by going to Scotland 

 and the Lake District : there being, so far as the speaker could 

 learn, no fossils in common with those of the typical locality, though 

 there were rocks in both places of the same physical character. 

 What had become of all these cubic miles of strata when we passed 

 from Rhayader to Llandovery ? The Author's paper was of great 

 value in raising these interesting questions. 



Prof. Groom congratulated the Author on an admirable piece of 

 work in a difficult district, but could speak only from a very im- 

 perfect acquaintance with the rocks of the Central Wales complex. 

 It would appear from the late Walter Keeping's list of graptolites 

 that the Tarannon Shales and the Upper and Lower May Hill Beds 

 were all probably present in the district ; but it had been reserved 

 for the Author to prove this, and show that the succession agreed 

 minutely with that of distant areas. A test of the accuracy of the 

 Avork might be found in the beautiful way in which it explained the 

 relations between the Silurian and Ordovician rocks, as stated by 



