Personal and Scientific News. 127 
mica is not the only character of this gneiss. It is, further- 
more, clearly divided into strata more or less thick which 
differ amongst themselves by their coarseness of grain, their 
richness in mica, the development more or less complete of 
crystallinity, the presence or absence of lenticular crystals of 
feldspar, the presence or absence of foreign elements, etc. 
This division into strata is everywhere very distinct in 
the lower, hence the older, portion of the formation. 
In the upper part the parallelism of the mica is less 
evident, the gneiss passes into granite, to granulyte and 
to pegmatyte ; and in certain parts of the /\rchean sheets of 
granite, of granulyte and especially of pegmatyte, alternate 
with crystalline schists. These latter are ordinarily glitter- 
ing, satiny or sericitic, with scales of white mica visible to 
the naked eye or under the loup. They are almost every- 
where ricli in minerals, and in certain cases they contain 
grains of quartz and thus pass to mica schist. Everywhere 
the true mica schists occur only exceptionally in the Py- 
renees, whether in the region of the gneiss or in that of the 
crystalline schists. 
Observation shows that at all horizons of the forma- 
tion of the gneiss are certain rare lentilles of crystalline tal- 
cose, chloritic or amphibolitic schists or of calcareous 
cipolins. 
Not only do we see in the upper portion crystalline 
schists alternating with gneiss, but in the mass of the gneiss 
itself can be seen inclusions of schists not completely di- 
gested. 
Everywhere the gneiss is in the form of lenticular 
masses ; everywhere it terminates as a wedge in the schists. 
At the points where it ends thus it can be seen to alternate 
sveral times with the crystalline schists, which on one side 
penetrate into the mass of the gneiss, while on the other it 
penetrates into the schists. This can be observed in all the 
exposures, but principally in the high valley of the Soulcen, 
one of the sources of the Vicdessos. 
All these facts prove that the gneisses and the schists 
of the Pyrenees are synchronous. / 
The geological map shows that the gneiss a])pears in 
the same places as the granite, although the two rocks do 
not mutually interpenetrate. They are both confined prin- 
cipally to that central ridge already mentioned and which 
occupies of itself a fifth part of the mountain chain. This 
ridge is replaced in the eastern part of the Pyrenees l)y the 
folds of the Canigau, Raz-Mouchet and Albere ; and it is 
these then that alternate with the gneis's. Another place 
where the gneiss and the granite appear is in those ridges in 
