139 



For an account of the various intrusive rocks, and for much in- 

 formation respecting the alluvial accumulations, including the mud 

 of the Nile and the changes of the Delta of that river, as well as of 

 the sand-drifts which have sterilized such large tracts, I must refer 

 you to the Memoir itself, which indicates great assiduity on the part 

 of the author, and who seems to have neglected no sort of informa- 

 tion which could he brought to bear upon the illustration of his 

 subject. 



After all, it must be allowed that, with the exception of the fossil 

 forest, and the recent elevation of her shores which separated the 

 Mediterranean from the Red Sea, Egypt presents fewer phseno- 

 mena to interest the geologist than any region of similar range over 

 which researches have extended; for this mass of land seems to have 

 been above the waters during the whole of the ancient periods of 

 which other regions afford such long registers in the contents of the 

 Palaeozoic and succeeding deposits. 



We have, however, but to advance northwards to the Lycian 

 Taurus, where Mr. E. Forbes has made known to us the elevation 

 to great heights of tertiary marine shells ; or north-eastwards to Syria, 

 where the Dead Sea, as now computed, lies upwards of 1300 feet 

 below the level of the Mediterranean, and we are furnished with 

 the most remai'kable proofs of the mighty oscillations to which the 

 surface has been subjected, even in recent epochs. In receding 

 from the Mediterranean to the Dead Sea, the Lake of Tiberias marks 

 the first depression, being 328 feet beneath the sea, and from this 

 lake to the Dead Sea the declination is nearly 1000 feet I A few 

 years back only and we were startled at the announcement, that the . 

 level of the Caspian Sea was 300 feet below the Mediterranean ; and 

 more accurate measurements have, indeed, reduced the depression 

 to 82 feet ; but that any cavity on a portion of the present surface 

 should be 1300 feet beneath the level of the adjacent seas, proves 

 an amount of vibration within a limited area, which is truly asto- 

 nishing*. 



Palaeontology. 



Ichthyology. — Geologists who have commenced their career since 

 the glacial theory has been in vogue and have read the numerous 

 memoirs and heard the exciting discussions to which it has given 

 rise, are chiefly acquainted with Professor Agassiz as one of its 

 most ingenious expounders. I have now the pleasure to acquaint 

 you that M. Agassiz is once more completely absorVjed in his great 

 work on fossil fishes — that work which you so justly honoured, in 

 the year 1835 to 1836, with your Wollaston Donation and Medal. 

 Of his progress in this arduous undertaking, he has recently given 

 substantial proofs, in the description of many ichthyolites of the Old 



* See the last discourse of Mr. W. Hamilton, the President of the 

 Royal Geographical Societ)-, who points out this admeasiu-ement as 

 being at length fixed by the admirable trigonometrical survey of Lieut. 

 Symonds, whose calculations of l.^ll feet approach very nearly to the still 

 higher estimate of M. Berthou, who, from barometrical observations, placed 

 it at 1332 feet. 



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