278 Reviews—Dr. Barrois’ Geology of Asturias, ete. 
published by the late Clifton Ward, which show a diminution of 
silica and increase of alumina in the zones of more intense 
metamorphisin. 
The quartz-porphyries, diorites, and diabases do not seem very 
abundant, and call for no special remark, but the recent quartz- 
kersantites form a curious group which, although they go into a 
small compass, have an extensive range. ‘The rock is essentially 
a crystalline compound of triclinic felspar, and black mica in a 
finely-granular or compact ground-mass, where there are generally 
grains of granulitic quartz, hornblende, and a pyroxenic mineral. 
Recent quartz plays a very important part, and titaniferous iron 
abounds; the occasional minerals being molybdenite, zircon, tour- 
maline, and even cassiterite. The latter is said to be abundant and 
to have been worked since the time of the Phcenicians. The occur- 
rence of this mineral in so recent a rock Dr. Barrois (p. 138) regards 
as a singular circumstance, having an important theoretical bearing. 
These kersantites he divides into (1) the granitoid, which are the 
most acidic, (2) the porphyroid, and (3) the compact. They differ 
in several important particulars from the old kersantites; the fel- 
spars, for instance, are fresh, and the iron mineral not hydrated. 
They are eruptive rocks, and their veins cut transversely and in all 
directions. “heir geological age is discussed in pp. 160-161, and 
the author finally concludes that they must have ‘made their 
appearance at the epoch of the great terrestrial dislocations which 
gave birth to the Pyrenees between the Eocene and the Miocene.” 
It is only just to remark that the mineralogical composition of 
several of the rocks, the kersantites especially, is beautifully illus- 
trated in plates i.— iii. 
Phenomena of modification.—Having interested his readers in the 
lithology, paleontology, and stratigraphy of the paleozoic and 
crystalline masses which aid in forming the Cantabrian Chain, Dr. 
Barrois finally discusses the influence of earth-movements and of 
denudation in fashioning the range itself. The history of earth- 
movements in times past must, in a great measure, be sought in 
mountain ranges, and in working out these fascinating speculations 
the author, as he admits, could have no better or more philosophical 
guide than M. de Lapparent. 
In the north of Spain the great earth-creep, whose effects can’ 
clearly be traced as having folded the strata, took place towards the 
close of the Paleozoic period, and there is no mention made of any 
previous movement of the first magnitude similar to that known in 
Belgium as the folding of the Ardennes, which occurred in Lower 
Silurian’ times; although minor oscillations are admitted to have 
taken place throughout the Paleozoic period. As a consequence of 
this freedom from movements of the first magnitude previous to the 
close of the Carboniferous, the lie of all the Paleozoic beds, including 
such portions of the Archean as are visible, is mainly N.—S., with 
prevailing dips to the W. The lie of the secondary formations on 
the contrary is E.—W., with prevailing dips to the N. The granite 
masses appear not to have influenced the position of the beds which 
inclose them. 
