ANNIVERSARY ADDRESS OF THE PRESIDENT. XCIX 



and that, the remaining portion of what is now the eastern end of 

 the English Channel was in the condition of dry land. The evi- 

 dence upon wliich the great changes which are shadowed forth in 

 this paper depend must be studied in the paper itself. I will only 

 further notice the theory of the brick-earth, which deserves atten- 

 tion, as Mr. Austen represents it as a subaerial deposit, produced 

 by the washing of the land at a time when there was a much heavier 

 rain-fall than at present ; but, as such wash is at present first directed 

 to the lines of watershed, and then by fluviatile action carried towards 

 the sea, forming the deltas of rivers, it still seems necessary to ex- 

 plain the position of the red earth, as a rain-deposit, in the several 

 sections given b}^ Mr. Austen. The paper is one of great interest, 

 on a subject of extreme difficulty, affording ample exercise both for 

 the industry and the ingenuity of the author. 



In my previous remarks I have pointed out, more especially in 

 drawing attention to the distinction which Mr. Sharpe had so ably 

 drawn between the ancient faunae of the north and south of Europe, 

 that at this epoch in geological science the great question is, not to 

 establish an identity between the natural history of distant areas of 

 the ancient surface of the earth, but rather to determine which of 

 many much-varied faunae and florge were actually of contemporaneous 

 origin. It is this change in the aspect of geological inquiry which 

 has rendered the correlation of strata a task of such extreme diffi- 

 culty as to have long exercised, as it will still exercise for many 

 years, all the penetration and cautious inquiry of Mr. Prestwich, 

 who seems specially fitted for a research which requires a combi- 

 nation of so much perseverance, so much patience, and so much 

 ability, and which resembles in difficulty the unfolding and decipher- 

 ing of some ancient papyrus scroll. In a former paper Mr. Prestwich 

 had expressed his opinion that the Eocene strata of France, Belgium, 

 and England were capable of subdivision, and that portions of each 

 might be identified as contemporaneous formations ; as, for example, 

 the Sables Inferieurs of France, the Landenian and Lower Ypresian 

 Systems of Belgium, and the Thanet Sands, Woolwich Series, and 

 London Clay might be thus classed together as deposits of the 

 earliest periods (in time) of the Eocene age. As the most remark- 

 able development of these deposits occurs in England, Mr. Prestwich 

 proposed for them the name of the " London Tertiary Group ;" and 

 I may remark in respect to this group, that the consequences which 

 might be drawn from the great thickness of these deposits within the 

 English area do not appear to have been fully considered. The 

 ordinary thickness exceeds 300 feet, but at one point at Portsmouth 

 it was found to be 600 feet, indicating therefore a great comparative 

 depression of the subjacent bottom either before or during the de- 

 position of this lower section of the Eocene strata. To this lower 

 section succeeded another, characterized by the rich fauna of the 

 Calcaire Grossier, and accompanied by a profuse exhibition of Num- 

 mulites, which had not been found in the underlying, or London, 

 group ; and to this section, on similar principles, ]\Ir. Prestwich gives 

 the name of the " Paris Tertiary Group." 



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