1848.] MURCHISON ON THE STRUCTURE OF THE ALPS. 187 



extends eastwards to Grand Bornand, particularly between Thones 

 and St. Jean de Sixt, you have on the left hand a ridge of neocomian 

 and cretaceous limestones overlapped by nummulitic limestone with 

 some of the schist of the flysch, and on the other side of the road 

 superior strata of the same series with hard sandstones in which con- 

 glomerates appear. There is no interval except that which has been 

 occasioned by denudation, and all the strata are conformable and 

 highly inclined, dipping to the S.S.E., the angle of inclination de- 

 creasing with the distance from the secondary limestones. At La 

 Sommerie, to the east of Grand Bornand and in a deep depression 

 under the Montague de Four, a lignite has been partially worked, 

 of the same age as that of Entrevernes near Aunecy, which is fairly 

 intercalated in the nummulitic group*. 



It is therefore evident, that even in the environs of Mont Blanc, 

 there is a connected section, which not only exhibits the whole suc- 

 cession of the cretaceous rocks properly so called, but also their up- 

 ward lithological transition into beds with nummulites ; and further, 

 that the latter are inseparable from the overlying flysch. The inde- 

 pendence, therefore, suggested by M. Favre does not exist in this 

 part of Savoy where the natural original relations have not been 

 effaced by dislocations. 



Now, these nummulitic and "flysch" strata, which by much more 

 developed natural sections in Switzerland, as well as by a consideration 

 of their fossils, will be proved to be a natural group, distmct from, yet 

 intimately and conformably linked on to the cretaceous system, are 

 copiously exhibited on the summits of some of the highest and least 

 accessible of the calcareous mountains to the north-east, north, and 

 west of Mont Blanc. Thus, rising to vast altitudes, they cap the 

 Dent du Midi and Diableretz, the former 9849, the latter 10,050 

 French feet above the sea. The fossils of the summit of the latter 

 have been long known to geologists, and besides Numftiulites globu- 

 lus (Leym.), the N. Biaritzana (D'Arch.) or regularis (Riittimeyer), 

 are the Cerithium diaboli (Brongn.), C. elegans (Desh.), C. poly- 

 meres (Leym.), together with AmpiUlaria, Chemnitzia, and the Me- 

 lania costellata (Lamk.), three of which are undistinguishable from 

 species of the Paris basin. 



In his admirable description of the rocks composing the summit 

 of the Diableretz, M. Brongniart not only enumerated nummulites 

 and several other fossils, and also indicated the intercalation with 

 them of a band of combustible in the condition of anthracite, but 

 he further justly reasoned on the nature of the shells and on the 



* This coal of Entrevernes is noticed by Bakewell, Travels in the Tarentaise, 

 vol. iv. p. 186, with M^oodcut. This author mentions Cythereae and Cerithia, but 

 does not alhide to NummuHtes. It was also visited by the members of the meet- 

 ing of the Geological Society of France which assembled at Chambery, when MM. 

 Charaousset, De Vernenil, Sismonda and Viquenel are reported to have foimd 

 tertiary shells associated with it. See Bull. Soc. Geol. Fr. 2nd series, vol. i. p. 214. 

 Coal of this age also occurs in the summit of the Diableretz (see next page) and 

 at Pernant on the Arve, where it was observed by Prof. Necker in both situations 

 associated with nummulites. For the latter position see Bibi. Un. de Geneve, 

 tom. xxxiii. p. 90. 



