Mr. R. Spruce on the Musci and Hepatice of the Pyrenees. 89 
tion, it rarely attains the surface in the neighbourhood of Bag- 
néres-de-Bigorre. Near Bagnéres-de-Luchon it appears m most 
of the valleys and at the base of the mountains. From the 
Central Pyrenees it passes into the Eastern, where, especially in 
the Dept. of Pyr. Orientales, it.constitutes a very large proportion 
of the surface. In the granite I include gneiss, and possibly some 
other rocks whose internal structure is of nearly the same cha- 
racter. 
-Mica-slate (schiste-micacé) I have observed in the Western 
Pyrenees only in the valley of Cauterets, especially at the base of 
the Monné and on Mont Lizé. Thence it passes into the Cen- 
tral district, where it constitutes the terminal cone of the Pie du 
Midi, the Pic de Mont-Aigu, and all the adjacent mountains. 
The wall of rock which supports the waters of Lac Lehou is of 
mica-schist, and in general the embankments of all the lakes in 
the Pyrenees are of this rock or of granite. In the Eastern Py- 
renees the mountains on the western side of the river Aude are 
of mica-schist, and I am not aware of its occurrence elsewhere. 
Slate (schiste-argileux) may be regarded as the most important 
_ rock in the Pyrenees, appearing as it does in every part of them. 
In the W. Pyrenees I have observed it in the Vallée d’Ossau ; also 
near Argélez, where it is the predominant rock, extending from 
thence along the gorge of Luz to the valley of Baréges, where it 
meets the mica-schist and other primary rocks. Ascending from 
Argélez by the valley of Cauterets, it extends (though not unin- 
terruptedly) to the very summit of the central chain. The Port 
de Cauterets and all the other passes which have fallen under my 
notice are (as in the Alps) excavated in slate-rock, which is often 
very siliceous, and cleaves with difficulty in at least two diree- 
tions. From Cauterets the slate passes into the Central Pyrenees, 
descending almost to their bases, and attaiming the ridge of the 
central chain, as at the Port de Bénasque, &c. In the Eastern 
Pyrenees it would seem to occur chiefly about the base of the 
mountains, skirting the granitic nucleus. The lower mountains 
in the Pyrenees, whose chief constituent is clay-slateor grauwacke, 
have commonly rounded summits, and are covered with herbage ; 
but the loftier ones, and especially those of the medial ridge, have 
a bolder aspect ; their sides are furrowed by deep ravines, and 
their summits are serrated and peaked. When closely examined 
they are found to be in a state of continual decomposition and 
degradation, probably from the dissemination of iron pyrites m 
these rocks. 3 
Transition-limestone (calcaire de transition) constitutes also its 
proportion of the surface of the Pyrenees. In the W. Pyrenees 
it forms the principal part of the ridge of the central chain, 
lying to the south of the Pic du Midi d’Ossau. From the val. 
