Cn. XVI.] NUHMUUTIC EOCENE STRATA. 3()7 



the valuable monograph published by him in 1853,* has observed 

 that a somewhat similar distribution of these and other species in 

 time, prevails very widely in the South of France and in the 

 Pyrenees, as well as in the Alps and Apennines, and in Istria — the 

 lowest nummulitic beds being characterized by fewer and smaller 

 species, the middle by a greater number and by those which individ- 

 ually attain the largest dimensions, and the uppermost beds again by 

 small species. 



In the treatise alluded to, M. d'Archiac describes no less than fifty- 

 two species of this genus, and considers that they are all of them char- 

 acteristic of those tertiary strata which I have called Middle Eocene. 

 In very few instances at least do certain species diverge from this 

 narrow limit, whether into incumbent or subjacent tertiary formations, 

 one or two species only, of which JVummulites intermedia, also a 

 Middle Eocene form, is an example, ascend into the Lower Miocene, 

 but it seems doubtful whether any of them descend to the level of 

 the London clay. Certainly they have never been traced so low 

 down as the marine beds, coeval with the Plastic clay or Lignite, in 

 any country of which the geology has been well worked out. This 

 conclusion is a very unexpected result of recent inquiry, since for 

 many years it was a matter of controversy whether the nummulitic 

 rocks of the Alps and Pyrenees ought not to be regarded as cretace- 

 ous rather than Eocene. The late M. Alex. Brongniart first declared 

 the specific identity of many shells of the marine Eocene strata near 

 Paris, and those of the nummulitic formation of Switzerland, although 

 he obtained these last from the summit of the Diablerets, one of the 

 loftiest of the Swiss Alps, which rises more than 10,000 feet above 

 the level of the sea. 



The nummulitic limestone of the Alps is often of great thickness, 

 and is immediately covered by another series of strata of dark-col- 

 ored slates, marls, and fucoidal sandstones, to the whole of which the 

 provincial name of " flysch" has been given in parts of Switzerland. 

 The researches of Sir Roderick Murchison in the Alps in 1847 have 

 shown that all these tertiary strata enter into the disturbed and lof- 

 tiest portion of the Alpine chain, to the upheaval of which they enable 

 us therefore to assign a comparatively modern date. 



The nummulitic formation, with its characteristic fossils, plays a far 

 more conspicuous part than any other tertiary group in the solid 

 framework of the earth's crust, whether in Europe, Asia, or Africa. 

 It often attains a thickness of many thousand feet, and extends from 

 the Alps to the Carpathians, and is in full force in the north of 

 Africa, as, for example, in Algeria and Morocco. It has also been 

 traced from Egypt, where it was largely quarried of old for the build- 

 ing of the Pyramids, into Asia Minor, and across Persia by Bagdad 

 to the mouths of the Indus. It occurs not only in Cutcb, but in the 



* Animaux Foss. du Groupe nummul. de l'Inde. Paris, 1853. 



