490 
THE GEOLOGIST. 
about thii-teen kilometres, or rather more than two leagues and a 
half.* 
In a letter, writen at Luchon, to M. Cordier, member of the Prench 
Institute, M. Leymerie gives a description of an ascent of the Muladetta, 
and of the different kinds of granite he has observed in the Pyrenees 
and in the Haute-Garonne. The ascent, which lies entirely over 
granite, can now be made in two days, by following the route indicated 
in 1842 by il. de Franqueville. The summit of the Muladetta, called 
le Pic de Nethon (the highest summit of the Pyrenees, and, ac- 
cording to Reboul, attaining to 11,443 feet), which, from the portof 
Venasque, looks so acute, consists in reality of a small plateau, com- 
posed of accumulated blocks and fragments of rock very similar to the 
accumulated fragments observed at the summit of Mont Perdu. 
The fundamental rock of the Muladetta is a small-grained granite, 
with white feldspar and nearly black mica, which M. Cordier has for- 
merly de scribed with great accuracy. But the summit of the Pic de 
Nethon offers a different kind of rock — a peculiar species, which may 
perhaps be classed between granite and quartziferous porphyry. In 
a quartzo-feldspathic cement of a dirty grey colour, the eye distin- 
guishes, on the surface of this rock, bits of grey quartz, scarce lamellas 
of mica, a few spots of amphibole and rectangular crystals of rose- 
coloured orthose (feldspar), which gives a rosy tint to the rock when 
viewed from a little distance. This last-named species of granite 
appears to predominate in the culminating parts of the mountain, and 
M. Leymerie supposes it to have penetrated through the former, which 
seems to have been uplifted in the solid state, together with the tran- 
sition strata which overlie it. 
The small-grained granite before alluded to must, therefore, have 
played a passive part in the formation of these high mountains, whilst 
the grey porphyroid variety has been the eruptive element. 
It is not so, however, with the porphyroid granite, bearing large 
macled ciystals of orthose, which forms the culminating portions of the 
Pyrenees from Maupas to Claribade, and which is very characteristic in 
the higher parts of the valley of Oo. This one, on the contrary, offers 
also unmistakeable eruptive characters. 
After a minute investigation of these rocks, the author comes to the 
conclusion that there are three principal sorts of granite rocks in the 
Pyrenees and the Haute-Garonne. 
1. The small-grained granite which might be termed, according to 
M. Leymerie, " granite Pyreneen," from its abundance in the Pyrenees, 
and which must be considered, in an eruptive sense, as passive. 
2. The porphyroid granite of the culminating points. And, 
3. The various granitic or feldspar rocks of Luchon, and the lower 
parts of the valley. 
The last two have played an active or eruptive part in the formation 
of the Pyrenees, and have produced veins, dislocations, unmistakeable 
phenomena of metamorphism, &c. 
The principal facts in the above have been extracted from a paper lately 
addressed to the Academy of Sciences at Paris, by L. F. Menabrea, entitled — 
Note sur le Peicemcnt des Alpes entre Modanc et Bardonlcke, which may be con- 
sulted by those of our readers who are desirous of further technical details. — T. L. P. 
