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, 
d prior, 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 hie old 
geologists to divide geognostic formations, then mostly studied 
in niguntain 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 débris. 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.: butit 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 Tine of 
direction. These exceptions occur in the chain of the Mont 
