Mr. R. Spruce on the Musci and Hepatica of the Pijrenees. 89 



tion, it rarely attains the surface in the neighbourhood of Bag- 

 neres-de-Bigorre. Near Bagneres-de-Luchon it appears in 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-micace) I have observed in the Western 

 Pyrenees only in the valley of Cauterets, especially at the base of 

 the Monne and on Mont Lize. Thence it passes into the Cen- 

 tral district, where it constitutes the terminal cone of the Pic 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 [schist e-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 Vallee d^Ossau ; also 

 near Argelez, where it is the predominant rock, extending from 

 thence along the gorge of Luz to the valley of Bareges, where it 

 meets the mica-schist and other primary rocks. Ascending from 

 Argelez 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 direc- 

 tions. From Cauterets the slate passes into the Central Pyrenees, 

 descending almost to their bases, and attaining the ridge of the 

 central chain, as at the Port de Benasque, &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-slate or 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 ravuies, 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 in 

 these rocks. 



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, 

 lyiug to the south of the Pic du Midi d'Ossau. From the val- 



