Changes in the Belative Level of Sea and Land. 305 



preservation as to freshness and colour, the bivalves, which 

 are identical with species now living near the shore of the 

 adjoining sea, retaining their uniting ligament ; indicating 

 that the changes have occurred, either during the latter part 

 of the tertiary period, or at the commencement of the exist- 

 ing geological period. These facts are described in the writ- 

 ings of Playfair, Von Buch, Keilhau, Sefstrom, Lyell, and 

 others, and some very remarkable cases have recently been 

 given in a memoir by M. Bravais,* who resided a year in 

 Finmark, between the seventieth and seventy-first degrees 

 of latitude, and who has measured with great care a series 

 of terraces or raised beaches in the Alton Fiord, which ex- 

 tend over a line of coast from fifty to sixty miles. 



The western coast of our own island has also, as you know, 

 afforded some most remarkable instances of these changes of 

 relative level of sea and land, from the north of Scotland to 

 Cornwall, and in some cases at a much greater elevation than 

 in Norway, as at Moel Tryfane in Caernarvonshire, more 

 than 1000 feet above the sea. That they have not been 

 found in as continuous extent in Britain as in Norway is 

 perhaps owing to this, that the shores of our island being 

 cultivated, these banks of loose materials would gradually 

 become obliterated. 



But it is not the shores of Europe alone that have afford- 

 ed proofs of these changes ; the continents of North and 

 South America exhibit them on a far grander scale, both on 

 the Atlantic and Pacific coasts. We are indebted to Mr 

 Darwin for descriptions of many remarkable instances ; and 

 some of these which have recently come again under our no- 

 tice, in the second edition of his " Journal,'' published within 

 the last few months, I will draw your attention to. I know 

 no geologist whose observations, and the inferences he draws 

 from them, are more to be relied upon ; for he examined the 

 country he describes evidently uninfluenced by any precon- 

 ceived opinions. They have, besides, a bearing upon some 



* A translation of this valuable memoir is given in the fourth number of the 

 Quarterly Journal of the Geological Society. 



