378 CARBONIFEROUS LIMESTONE OF THE MENDIP AREA. [May I906, 



Plate XXXIII. 



Sketch-map, showing the outcrop of the Carboniferous Limestone (Avonian) 

 in the Mendip area, on the scale of 4 miles to the inch. 



Plate XXXIV. 



Range-diagram of corals in the Carboniferous Limestone (Avonian) of the 

 Mendip area. 



Plate XXXV. 



Range-diagram of brachiopods in the Carboniferous Limestone (Avonian) of 

 the Mendip area. 



Discussion. 



The President said that he had already expressed his interest in 

 the application of Dr. Vaughan's work to other districts, and he 

 congratulated the Author on the clearness with which he had 

 presented his results to the Fellows. 



Mr. W. A. E. Ussher complimented the Author on the working- 

 out of the tectonic features of the Men dips, a point which was 

 not contemplated in the resurvey of the area by himself and 

 Mr. H. B. Woodward about 34 years ago. In view of the abnormal 

 occurrence of Coal-Measures under the Carboniferous Limestone at 

 Yobster, he desired to ask the Author as to the exact position of 

 the borehole in the Ebbor Valley, in which Coal-Measures were 

 said to have been struck. 



Mr. H. B. Woodward wished that the Author had marked on the 

 map the boundaries of the zonal divisions. With regard to the 

 Ebbor district, he was quite prepared to accept the Author's reading 

 of the structure, which differed from that to which he had been led 

 in 1871 ; and he thanked the Author for dealing generously with 

 the work of those who had. preceded him. 



Mr. E. E. L. Dixon congratulated the Author on the valuable 

 results obtained by his determination in the Mendips of the zones 

 instituted by Dr. Yaughan. In view of their proved general ap- 

 plication in Western England, Wales, and Ireland, these zones 

 might be considered as having passed beyond the probationary stage, 

 and future advances would trend in the direction of determining by 

 their means the physical conditions at various periods of Carboni- 

 ferous time, and in unravelling the evolutionary connexion between 

 successive faunas, as it was on this connexion that the value of the 

 zoning method depended. 



The district described was of especial interest to the speaker, as 

 the change in the character of the Syringoihyris-Zone, which was 

 noted in passing northwards from it to Bristol, could be paralleled 

 in Southern Pembrokeshire, where fossiliferous limestones in the 

 lower part of the zone gave place northwards to a band of dolomites 

 on the same horizon. Another point of interest was the absence 

 of any sign, below the base of the Avonian, of the approach to the 



