500 Notes on the Pyrenees, 



At the Tour de Soube the granite, topped with alpine lime- 

 stone, crops out above the transition series, attaining an eleva- 

 vation of 1607 toises, forming in this case the crest of the 

 chain. The transverse chains are constituted of transition 

 rocks, reposing on older formations. Transverse chains, of a 

 structure similar to that of the crest at their departure, may 

 in their course be overlaid by other rocks : thus, the mica 

 slate overlies all the transverse chain of granite originating 

 between the Port d'Estaubas and the Port de Clarabide, as 

 the transition rocks overlie the mica slate a little further 

 down the chain. As mica slate is only met with associated 

 with granite rocks, so the primitive limestone is only seen 

 forming detached masses on the same mountain rock, nor can 

 its distribution be at all associated with any of the physical 

 phenomena exhibited by the mountain chain. 



No chains occur in the Pyrenees, following a direction per- 

 pendicular to the principal crest, which are not either attached 

 to it or to other parallel chains ; and we believe that this fact 

 is applicable to mountain chains in general. We do not think 

 that the difference of formation, or the absence of any hilly 

 connection between two parallel chains in the immediate 

 vicinity of one another, can satisfactorily establish their inde- 

 pendence ; but the isolation of a transverse chain would always, 

 a priori, decide upon its local geographical relations, in most 

 countries of mountains and mountain chains. There occur on 

 the lateral limits chains of a different structure coursing pa- 

 rallel to the principal crest. This fact led one of the old 

 geologists to divide geognostic formations, then mostly studied 

 in mountain chains, into bands : Guettard describes a sablo- 

 nous band, a marly band, and a schistose or metallic band ; 

 and the Pyrenees present features very nearly allied to these 

 views. These inlying chains are in most cases formed of rocks 

 or deposits of a more modern formation than the principal 

 crest, of which they are oftentimes the debris. Bourguet, in 

 his Phenomena of the Constitution of the Globe, says, the chains 

 extending from east to west have sometimes shells and plants 

 on them ; while their branches, extending north or south, are 

 entirely formed of fish, shells, plants, &c. : but it is difficult 

 to say whether he was alluding to their real direction with 

 respect to the meridian, or to the relation of lateral and of 

 transverse chains to one another. 



In the Pyrenees parallel chains are generally of a structure 

 different from that of the principal : they are chiefly consti- 

 tuted of alpine or Jura limestone, the former of which, with 

 few exceptions, always forms hills having a similar line of 

 direction. These exceptions occur in the chain of the Mont 



