102 PALEOZOIC EOCKS OP THE KILBEIDE P£KI]S'SULA. [Feb. I9I2, 



one another, the only difference being perhaps a little coarse texture 

 in the case of the Welshpool bostonite. 



It was a most unsatisfactory circumstance that, in practically 

 every case where Trinudeus had been recorded from Silurian rocks, 

 something was left opeo to doubt. Here it had turned up in a 

 wall-fragment. It was, however, of such importance that he 

 thought it would be very advisable for the Authors to give a 

 separate list of the fossils associated with it in the fragment. 



Dr. H. Lap\yorth said that he was interested in the comparison 

 of the Llandoveiy rocks in the West with their equivalents in the 

 ISTorth-East of Ireland. In the former region they appeared to be 

 of the arenaceous type as developed at Llandovery itself, along the 

 Welsh Borders, and in the Girvan area in Scotland; in the other 

 region they were of the graptolitic-mudstone facies, as found in 

 ISTorth-West Wales, the Lake District, and the Southern Scottish 

 Uplands. With further work in Ireland and Wales, it would 

 become possible to trace approximately the limits of the original 

 deep-sea trough. 



With reference to the Authors' geological map, he was struck by 

 the amount of detail inserted along the faulted southern margin, and 

 on what he assumed was a 6-incli plan. He would be interested 

 to know whether the exposures were so numerous as to enable 

 the Authors with certainty to develop the detailed structure 

 shown. 



Dr. J. V. Elsden called attention to the resemblance mentioned 

 in the paper between the Kilbride keratophyre and the lime- 

 bostonite described by him from Abercastle, in Pembrokeshire. 

 Prom his examination of the specimens exhibited^ he thought that, 

 while there seemed to be points of similarity, there were also 

 important differences. He would like to see a chemical analj'sis 

 of the Kilbride rock. The felspar in this rock was described as 

 albite, while that in the Abercastle variety seemed to be oligoclase. 

 Eeferring to the general question of the nomenclature of these rocks, 

 he had submitted specimens of the Abercastle rock to Prof. W. C. 

 Brogger, who, while not denying its general mineralogical and 

 chemical resemblance to the typical majnaite or lime-bostonite of 

 the Gran district, was disposed to exclude the Abercastle specimen 

 from that class on account of its associated rocks. In the speaker's 

 opinion, however, the introduction of genetic affinities greatly 

 increased the difficulties of rock-nomencbture. 



Mr. C. I. GAEDiisrER thanked the President and Pellows for the 

 way in which they had received this communication. He assured 

 them that the paper would include chemical analyses. As attention 

 had been drawn to the large number of more or less parallel faults, 

 which were seen on the 6-inch map to displace the Silurian strata, 

 he pointed out that, owing to the fact that there was a red sand- 

 stone near the base and higher up in the series dark calcareous flags 

 covered by purple shales, it was a comparatively easy matter to map 

 in the faults represented, as the exposures were very numerous. 

 The Authors were quite confident that the faults really existed as 

 mapped. 



