the Mountains of Scotland. 8) 
planes of orientation are independent of the primitive foliation, 
which they cut across, and sometimes obliterate completely, and all 
the staves of the changes can be followed. It will be seen, since the 
original foliation here plays no part, that the result would have been 
the same in a granite; one is assisting, in fact, at the formation of 
gneiss, and of amphibolic schists, by means of the foliation of granitoid 
rocks. This theory has already been several times proposed, and 
has been cited in support of other observed facts; but I do not think 
that any of these facts can present themselves more clearly or offer 
an easier verification than those under consideration. 
It may be objected that the effect is produced in narrow areas 
only; but it is so by a phenomenon which is only exceptionally 
localised, and which, from what is known of its other effects, is 
capable of extension over masses of almost indefinite size. One is 
thus in a position to conclude that the foliation of eruptive rocks 
is one of the possible and even probable modes of formation of 
eneiss. In the first place, as has been seen already, the same 
mechanical metamorpbism may be applied to sedimentary rocks. 
Moreover, M. Michel Lévy has proved that the injection of eruptive 
into sedimentary rocks can equally produce true gneisses: perhaps 
only in this case is it less easy to conceive of the extension of the 
phenomenon to vast areas. Lastly, there may be gneisses formed 
originally and directly in the state of gneiss, corresponding in such 
a case to the first crust of the solidified globe. Dr. A. C. Lawson has 
described an interesting example of this in Canada, which would 
approximate this mode of formation to that of the eruptive rocks. 
Here are, then, three possible origins, outside all theory, and it 
must be owned that choice, in the present state of knowledge, is 
very seldom possible for each particular case. The observations of 
Messrs. Peach and Horne mark, however, a further step towards the 
solution, and what L. von Buch said of the Tyrol may be repeated 
here. All geologists who take up these questions should make a 
pilgrimage to the Scottish coast. 
In concluding this summary, it remains to me to express the 
desire that these beautiful discoveries may be, as soon as possible, 
published in all their details. The Report of 1888 is but a résumé 
of the most important facts; one has a right to expect, and to 
demand, a complete monograph. All the elements of such a 
monograph will soon be gathered together; they must be made 
public. It is desirable that a micrographic study should accompany 
and give precision to all the observations relating to metamorphism, 
and especially that it may be possible to follow the perusal of the 
Memoir on detailed maps. An immense amount of labour has been 
undergone in carrying out this survey: the reduction to a scale one- 
sixth of that of the original maps will cause an almost inextricable 
complication of lines, and the loss of the benefit of part of the 
work. ‘The region presents an interest sufficiently exceptional, and 
sufficiently general, to raise it above the rules of ordinary routine, 
and the question of cost is not an obstacle. England is rich enough 
to pay for its glory. 
DECADE IlI.—VOL. X.—NO. III. 9 
