AND EOCENE STRATA. 643 



the true clue to tlieir relation clearly exhibited in unmistakable and 

 perfect sections ; the importance of which clue in its bearing on conti- 

 nental geology may be estimated very highly." 



The opinion of my late lamented friend, so emphatically expressed 

 in this passage in favor of the classification which I formerly adopted, 

 will convince every reader that the old nomenclature might be defended 

 by many cogent arguments ; and some of these M. Deshayes has lately 

 set forth in the prelimiuary chapter of his supplement to "The Fossil 

 Shells of the Paris Basin ;"* *where he says, that while, on the one 

 hand, the dissimilarity is enormous between the fossils of the Fontaine- 

 bleau Sands and those of the faluns of the Loire, we find the fauna of 

 the former to be allied to that of the marine beds below the Paris gyp- 

 sum by a predominance of certain genera of shells. These he enumer- 

 ates, and his observations are in harmony with what I have said (p. 

 184) respecting the "Eocene aspect" of the testaceous fauna of those 

 strata which occupy the debatable ground. 



Notwithstanding these and many other arguments which might be 

 adduced in support of the classification formerly advocated by me, and 

 given in my Table at pp. 104-5, I have come to the conclusion that it 

 will be more convenient to draw the line of separation in the place so 

 generally adopted in France, provided that we always regard it as an 

 arbitrary and purely conventional line, — one which has no pretensions 

 to be founded on any great change of species, still less on any general 

 revolution in the earth's physical geography assumed to have happened 

 at the era referred to. The classification was originally suggested in 

 France by an accidental break in the regular succession of marine 

 strata, caused by the intercalation on the site of Paris of certain fresh- 

 water gypseous marls, in which the Paleothere and other quadrupeds 

 were discovered. By these marls the marine sands of Beauchamp, often 

 called the "Sables Moyens," were separated from the marine sands of 

 Fontainebleau. In countries where no such interruption occurs, the 

 series, whether composed of freshwater, fluvio-marine, or marine strata, 

 will exhibit " beds of passage" between Eocene and Miocene, such as 

 those of Hempstead, in the Isle of Wight, or those recently discovered 

 in the Alps by MM. Hebert and Renevier, and described by them in the 

 Bulletin of the Statistical Society of the Department of the Seine 

 (1854). In this interesting memoir an account is given of a formation 

 termed by the authors " the Upper Nummulitic," which occurs in the 

 neighborhood of Gap, and in the Diablerets in Savoy, where the Ceri- 

 tliium 2^licatum and other shells usually accompanying it in the Fon- 

 tainebleau Sands and in Belgium are abundantly intermixed with spe- 

 cies frequent in the Gres de Beauchamp, and even in the inferior Cal- 

 caire Grossier. Here, therefoie, we have an example, among the 

 highly elevated and contorted strata of the Alps, of marine beds of pas- 

 sage of the period under consideration, remarkable for many reasons,, 



^ Description des Animaux sans Veitebres, &c. Paris, 1857, p. 17. 



