90 Mr.R. Spruce on the Musci and Hepatice of the Pyrenees. 
ley of Cauterets it would seem to be entirely absent, but it re- 
appears in the Central Pyrenees in the great valley of Baréges, 
where it extends from the bottom of the valley of Gédre to a little 
beyond the lake of Gavarnie, and plunges under the immense 
mass of alpine limestone of the Marboré. The lower hills near 
B.-de-Bigorre, especially the Pie de Lhieris, are formed almost 
entirely of it, and here it often presents itself in thin beds, alter- 
nating with clay-slate. In the upper part of the valley of Lu- 
chon, and in all the surrounding mountains, I do not recollect 
to have observed any calcareous rock. In the E. Pyrenees, 
transition-limestone would seem to occur amongst the granitic 
formations in detached masses (accompanied however by slate) 
chiefly in the neighbourhood of Villefranche and Prats de Mollo, 
and in the Corbiéres. The ascents of mountains of transition- — 
limestone are interrupted by escarpments, which are rarely of 
great elevation. | 
Of secondary rocks, the only one which I shall have oceasion 
to mention is oolitic limestone (calcaire alpin). To this rock the 
Pyrenees owe some of their grandest features, as it forms escarp- 
ments in some instances. considerably exceeding a thousand feet 
in altitude, as at the Cirque de Gavarnie, the termination of the 
Vallée d’Estaubé, &c. ; but wherever it attains the alpine region 
(as in the instances just cited) I have found it quite destitute of 
mosses, probably from its exposed position, above the region of 
forests. It is only in the lower hills of the Western Pyrenees, 
especially near Pau, where it occurs as a conglomerate, that the 
alpine limestone has afforded me any cryptogamia. © Some of 
Dr. Arnott’s mosses from the Pyr. Orientales, judging from the 
fragments attached to the specimens, have been gathered on 
alpine limestone. 
Trap-rocks I have remarked in the Pyrenees in small detached 
masses, but I have gathered cryptogamia only on a rapidly de- 
composing ophite at Labassére near B.-de-Bigorre, and at St. 
Pandelon near Dax. . 
This brief sketch of the chief rocks of the Pyrenees is confessedly 
very imperfect ; it is also designedly superficial, for it is only by 
the surface-rock that plants whose roots rarely penetrate to the 
depth of an inch can possibly be influenced. The position, too, 
of any rock in the geological series cannot be said to have any- 
thing to do with the distribution of plants, though the presence 
of a certain mineral is in many cases essential to their existence. 
From my observations in the Pyrenees and elsewhere, I have 
ascertained pretty accurately what mosses require a matrix con- 
taining carbonate of lime; these will be specified as they occur. 
They have obviously no preference for primitive, transition, or 
secondary limestone, but they are always most abundant and 
