164 CAEBONIFEEOTJS LIMESTONE IN SOUTH WALES, [vol. Ixxili. 



large a scale to be atti'ibuted mainly to material leached out of the 

 contemporaneous dolomites, although some such redistribution of 

 dolomite had doubtless taken place. 



He had not anticipated that this would be made the occasion of 

 an attack by Dr. Grroom upon the interpretation of the succession 

 in the Forest-of-Dean Coalfield which he (the speaker) had published 

 more than four years ago. He adhered in every particular to the 

 conclusions then published. The unconformity was quite unmis- 

 takable. It was evidenced by continuous transgression of the 

 Coal Measures across the Lower Carboniferous strata (Carboni- 

 ferous Limestone and Drybrook Sandstone) on the northern and 

 eastern borders of the coalfield; by a great difference in the 

 inclination of the two series of strata all along the eastern margin 

 from Mitcheldean to Howbeach ; and incidentally by marked 

 angular discordance at the junction exposed in an old quarry 

 near Howbeach Colliery. Dr. Groom, by admitting the existence 

 of 'a gentle unconformity at the base of the Coal Measures,' 

 invalidated his own objections to the speaker's interpretation of 

 the structure. As a fact, the attitude of the Lower Carboniferous 

 strata determined a change from slight discordance with the 

 Coal Measures on the northern edge of the coalfield to pronounced 

 discordance on the eastern edge. The featm'es in the Blackpool 

 Valley were due, not to faulting as maintained by Dr. Grroom, 

 but to rapid, unconformable overstep by the Coal Measures. A 

 mass of further evidence, collected by the speaker since 1912, 

 could be adduced to confirm his reading of the succession in the 

 Forest of Dean ; but, on account of the lateness of the hour, 

 he would not pursue the subject further. 



[August 20th, 1918.] 



