70 messes. w. e. andeews and a. j. jukes-beowne [feb. 1 894, 



Discussion. 



The President said that the Society was much indebted to the 

 Authors, and especially to Mr. Andrews, for details as to these beds 

 which he alone could furnish. He (the President) had often received 

 assistance from Mr. Andrews when he was working at the Porthmd 

 Beds of the Vale of Wardour, but that gentleman could never interest 

 him in the Purbecks of the locality — a somewhat monotonous series, 

 with fossils too often flattened to be recognized. The difficulties of 

 investigation were considerable ; hence the old view that the Wardour 

 Purbecks did not exceed 70 feet, whereas the Authors considered 

 that they had demonstrated a thickness of 170 feet. In the Vale of 

 Wardour there were no fine cliff-sections as in Durleston Bay, and 

 the entire series had to be constructed by piecing together the 

 exposures in different quarries. 



The Authors had adduced additional palseontological evidence, 

 which, in his opinion, tended to strengthen the view that the 

 Purbeck. taken as a whole, could scarcely be called a freshwater 

 formation. Inroads of the sea were perpetually replacing the 

 freshwater fauna by estuarine or marine forms, and such species as 

 Trigonia gibbosa and Cardium morinicum seemed to indicate that a 

 Portlandian fauna was close at hand. Both in the Lower and 

 Middle Purbeck Beds these marine horizons were well-marked, and 

 it was extremely interesting to find that the Authors could correlate 

 them with the developments in Dorset. The most novel feature 

 was the discovery of Upper Purbeck strata : these sandstones with 

 Eiulogenites had little in common with the Upper Purbeck of Dorset, 

 and had usually been regarded as of Wealden age. Indeed the 

 Authors admitted that the conditions were Wealden, but the Cyprids, 

 as determined by Prof. T. Rupert Jones, were held to indicate 

 Purbeck affinities. 



Prof. J. F. Blake remarked on the great value of the paper. He 

 had not been able to accept the idea of the junction with the Port- 

 land being in the middle of a block, and was glad to find that the 

 Authors also declined to accept this line. On general principles he 

 considered that, unless there was a physical change accompanying a 

 faunal one, the latter was of secondary importance. Palaeontology 

 must be the servant and not the master of Geology. He thought 

 the Purbecks of the Vale of Wardour were really locally uncon- 

 formable on the Portlands, and had been laid down in a separate 

 lake or estuary not directly connected with that of Dorset. He 

 enquired as to the overlying Cretaceous rocks, because on their 

 con form ability or otherwise would depend the Upper Purbeck or 

 Wealden character of the highest beds described. 



Prof. T. Rupert Jones, in explanation of the conditions of the 

 Lowest Purbeck ' flaggy limestone ' and its conterminous strata, 

 thought that the Portlandian sea, in giving way to the shallowing of 

 the coast, and the local predominance of freshwater lagoons, must 

 have been rough enough at times to break up the changing floor, 

 disturb the new deposits, and make a kind of unconformity, accom- 



