^76 



Reports and Proceedings. 



horizon as the uppermost Plattendolomite of the Zech stein formation 

 in the Harz and Thuringia. Above this lie the lowermost beds of 

 the Bimter (containing dolomites), and below it the upper part of the 

 Zechstein formation. Below the Plattendolomite of the Zechstein, 

 from the depth of 1,740 feet to 1,884 feet, follow the saliferous beds. 



Discussion. — Sir K. I. Murchison differed from the author, inas- 

 much as he regarded the whole of the dolomite rocks mentioned as 

 belonging to the Permian system, and not to the Bunter Sandstein 

 proper. 



3. "On the formation of Deltas ; and on the evidence and Cause 

 of great Changes in the Sea-level during the Glacial Period." By- 

 Alfred Tylor, Esq., F.L.S., F.G.S., &c. 



The first portion of this paper was devoted to a comparison of the 

 delta-deposits of the Po, Ganges, and Mississippi. The surfaces of 

 these deltas and the alluvial plains above them were compared to- 

 gether ; and it was stated that a parabolic curve drawn through the 

 extremities of each river, and through one point in its course, nearly 

 represents its longitudinal section — the greatest deviation being 30 

 feet in some of the largest deltas. 



The littoral deposits around Great Britain described by Mr. God- 

 win-Austen were next investigated, to ascertain whether the hypo- 

 thesis of a fall of 600 feet in the sea-level is tenable. The ice-cap at 

 the poles was also alluded to as a probable cause of a great reduction 

 of the sea-level during the Glacial period. 



The upper 600 feet of deposits in the Pacific Ocean, made by coral- 

 zoophytes, were quoted as cases which might be explained as well 

 by oscillation in the sea-level as by the received hypothesis of the 

 subsidence of the sea-bottom. 



Prof. E. Forbes's investigations into the origin of the fauna and 

 flora of the British Isles were next alluded to, and the author con- 

 sidered that the hypothesis of a fall in the sea-level better accords 

 with the facts of migration than Forbes's suggestion of changes of 

 the level of the land and sea-bottom. 



The origin and age of the English Channel was discussed at some 

 length ; and the occurrence of the Crag and fossiliferous gravels and 

 raised beaches near the same level, although of different ages, to- 

 gether with the evidence afforded by the dredging up of fresh- water 

 and littoral shells in the North Sea and English Channel, were ad- 

 duced in support of the theory of the depression of the sea-level. 



The parabolic curve not only represents the curve of deposition ; 

 for the author had measured other sections, and found that the curves 

 of denudation and deposition approximate often to that of the parabola. 



Discussion. — The President called attention to the fact that in the 

 neighbourhood of coral reefs the dead corals extend to such a vast 

 depth that, supposing them all to have been formed near the surface, 

 and that surface only lowered by abstraction of water to the Poles, the 

 accumulation of ice must have been so great as to become incredible. 



Sir Charles Lyell had already suggested to Mr. Croll that, assuming 

 the accumulation of ice at the Pole depressing the centre of gravity 

 of the earth, the submergence that would have resulted, had the 



