Excavation of Valleys. 35 



explain our reasons for offering any additional remarks on the 

 subject. In the earliest of these publications, Messrs Deveze 

 and Bouillet have described the series of strata in which the 

 bones of extinct quadrupeds have been found, as overlaid by a 

 mass of ancient basalt, and they have cited Dr Buckland as co- 

 inciding in opinion with themselves; but they were mistaken 

 on that point, for the Professor was well known to have come 

 to an entirely opposite conclusion. We find also that some of 

 our own views on these extraordinary phenomena are not in ex- 

 act accordance with those of any of the numerous observers who 

 have as yet written on the subject.* 



The nucleus of Mont Perrier consists of tertiary strata, which 

 appear to have been once covered by an uniform mass of an- 

 cient basalt, by which, as represented in Desmarest's map, the 

 western portion of the hill is still capped. Towards the east, it 

 now descends with a gradual slope into the gi'eat alluvial plain 

 of Issoire, this part of its surface being strewed with blocks of 

 the same basalt in a state of disintegration. This sloping portion 

 is deeply cut into by several ravines running from west to east, 

 in one of which, near the farm-house of Boulade, occurs the 

 chief deposite of bones, the geological position of which has given 

 rise to so much discussion. 



We shall first describe, in an ascending series, the strata met 

 with between Issoire and the ancient alluvion near Bouladef , 

 and afterwards other sections on the north-western escarpment 

 of the hill, — the latter of which can alone elucidate the relations 

 of the superficial deposites to the older strata. The lowest rock, 

 in ascending from Issoire, occurs at Les Chapelles. It is a 

 granitic aggregate, containing occasionally rounded fragments 

 of quartz, gneiss, and mica-slate ; and has been called Granite 

 by Messrs Deveze and Bouillet, and also subsequently by 

 Messrs Jobert and Croizet, from which, in hand specimens, it 

 may often be undistinguishable. This rock is worked into 



" The most recent of the two works alluded to, is entitled, " Recherches 

 sur les Ossemens Fossiles du Puy de Dome," and has already been cited by us, 

 p. 22, in a manner which shews that we accord with the authors Messrs 

 Croizet and Jobert in many essential points. 



+ See Plate II. 



C2 



