230 
Proceedings of the Royal Irish Academy. 
subsequent to the publication of our memoir"^' seem to show that rocks 
belonging to this stage, and to the other associated Jurassic rocks, 
extend over the whole peninsula, and probably crop up along the 
slope of the Dzurjura range of the Atlas mountains, on the African 
side of the Mediterranean . Indeed, one cannot help being struck at 
the similarity between the descriptions of the several districts thus 
independently examined. While on the one hand they clearly demon- 
strate that the age of several of the groups of rocks constituting the 
great mountain chains of Spain, Portugal, and JN^orth Africa remain 
to be definitely settled, and brought into connexion with the better 
studied ranges of the rest of Europe, on the other, there can be no 
doubt of the important position which Jurassic rocks occupy among 
those groups. On both sides of the Mediterranean we find rocks of 
this period forming mountain chains as lofty as the Pyrenees, and 
under conditions and presenting lithological and physical characteris- 
tics which give considerable support to our views regarding the age of 
the Picos de Europa. 
When discussing the age of the rocks composing the Picos de 
Europa we overlooked an important admission of Don G. Schultz, 
which shows that, although he coloured in his geological map the 
greatest part of Eastern Asturias as carboniferous, he was very far 
from believing that the age of the rocks of that district had been 
determined. Indeed, when we consider his uncertainty as to the 
exact nature of the silurian period, the basis, so to speak, of his 
whole stratigraphical scheme, the extraordinary positions which 
he assigns to the carboniferous rocks in many parts of Asturias, 
at one time unconformable, and at another conformable, or even 
actually interpolated in, or underlying devonian rocks, and the 
similar confusion between certain so-called keuper and carboniferous 
rocks, it is evident that the geology of the eastern parts, if not of 
the whole of Asturias, requires to be re-examined. 
The passage in Don G. Scliultz's work to which we have referred 
is as follows. After stating how difficult it is to distinguish in the 
carboniferous rocks an order of succession or of age, he says of the 
eastern part of Asturias : — We cannot state with certainty that the 
devonian does not crop out in some one or other point of this vast 
mountainous region which we have gone over ; it is rather to be sup- 
posed that it exists in some of its valleys or in the masses of quartz- 
ite intercalated among the beds of the carboniferous formation in 
the same way (or rather in the inverse) as we have seen the carboni- 
ferous formation interposed between beds of the older formation, nor 
* See, among others, Coquand's Meraoire sur la province de Castillon de la 
Plana (Bulletin dela Societe Geologique, t. xxiv., 1866-67); M. E. Jaquot, sur 
la composition et sur I'age des assises que dans la peninsule Iberique separent la 
formation carbonifere des depots jurassiques. — Ibid.; M. Maris, sur les roches for- 
mant les sommets de la Grande Kabylie. — Ibid. t. xxv., 1867-68 ; Notes on the 
Geology of the Province of Jaen, Revista Minera, 1868, p. 311. 
