Reviews—Dr. Barrois’ Geology of Asturias, ete. 273 
It has been observed in all areas where the Archzan rocks are 
developed that no minute order of succession can be made out, but 
in many areas the following general succession occurs in ascending 
order :— : 
1. Highly metamorphosed, often foliated rocks. 
2. Less highly metamorphosed rocks, rich in green silicates, and 
often foliated. 
3. Unmetamorphosed lavas and ashes. 
The rocks (2), according to the supposition of their voleanic origin 
above advocated, would, as already explained, be merely the same 
rocks as (1) which had not been sufficiently deeply buried to become 
so highly altered, and it is noticeable in connexion with this that 
they are usually less penetrated by granites. 
The rocks (3) would be formed, as described, after the removal of 
much of (2) and some of (1) by denudation, and we may therefore 
expect to find them resting sometimes on (2) and sometimes on (1) 
and presenting discordance of dip with these. 
Lastly, the various doubtful unconformities which have been 
recorded in the Archzean rocks may be in many cases due to denu- 
dation of the volcanoes during periods of comparative volcanic 
quiescence, and the accumulation of agglomeratic fragments perhaps 
rounded by pluvial action upon the eroded surfaces of the older 
pyroclastic rocks. 
This view of the origin of the Archean rocks is of course only to 
be confirmed or otherwise by rigid microscopic examination of the 
rocks themselves, but I have thought that it would be useful to draw 
up these notes in order to show how many actual difficulties do occur, 
which there is often a tendency to overlook. 
a5¢, Jah Wade eH WW Se 
—_.——_ 
I.—Dr. Barrors’ GroLtocy oF THE OLDER Rocks oF THE ASTURIAS 
AND GALICIA. 
(Secon Norice.) 
VHE Lithology of this fine work has evidently received most 
careful attention on the part of the author, and hence we find 
that this portion of the subject has the post of honour assigned to it, 
whilst the book itself is dedicated to the well-known petrographers, 
Messrs. Fouqué and Michel-Lévy, in acknowledgment of the assist- 
ance obtained from the College of France in this department. Dr. 
Barrois chiefly concerns himself with the lithology of the paleeozoic 
schists and quartzites, and with that of the massive crystalline rocks ; 
but in the stratigraphical portion of the work the description of the 
“terrain primitif” (Archean) is so essentially based on its mineral 
composition and rock structure, that this also falls within the litho- 
logical section, although relegated to an entirely different chapter 
(pp. 3887-406). 
We have then to consider three divisions of the subject, and it may 
DECADE II.—VOL. X.—NO, VI. 18 
