128 Notices of Memoirs—Prof. M. Bertrand— 
studying is succeeded by another where reigns the appearance of the 
most complete calm, where the gneisses themselves are but feebly 
and gently undulated, where the sandstones which overlie them have 
almost everywhere remained horizontal. These sandstones (Torridon 
Sandstone), of which I have already said one word, recall the aspect 
of our Permian stage by their coarsely detrital nature and by their 
red and brown colour; in their entire thickness, which is great, 
there is no trace of metamorphism. They are, however, incon- 
testably older than the Cambrian quartzites everywhere to be seen 
resting unconformably witha slight dip to the east on the slices of the 
obliquely cut horizontal sandstones. Hrosion has deeply sculptured 
these sandstones into isolated peaks of quaint and abrupt shapes, 
like immense fortresses guarding the coast-line; strangers, as 
MacCulloch said—the first geologist who described them—by their 
nature and by their structure to all that surrounds them, they seem 
astonished to find themselves where they are. Their horizontality, 
their freshness, their resemblance to more recent deposits, these are 
so many indications that the basement on which they rest has itself 
remained much as it was in those ancient times. What can be 
studied at their base then are the gneisses such as they were before 
the Cambrian epoch. 
This is a point of great importance; it is owing to circumstances 
of this kind that the study of the gneisses will always be easier and 
more fruitful in more northern countries than in ours. Where the 
Harth’s crust has been dislocated up to more recent times, the 
gneisses are only exhibited to us with all the transformations due to 
metamorphism and to the successive injection of igneous rocks. It 
does not appear that this complexity has given rise to special types 
(though I do not think that a serious study, without preconceived 
views, has yet been carried out in this direction); but at any rate 
such a complexity renders it more difficult to assign to each agent 
the part it may have played. Where on the contrary, as in Scotland, 
deformation has stopped at its first stage, the problem is simplified, 
and the chances are greater that precise conclusions may be arrived at. 
The gneisses of the Scottish coast are basic gneisses, in which the 
mica is replaced by amphibole or pyroxene; they are granitoid 
gneisses, t.e. the arrangement of the dark-coloured materials along 
parallel lines is but faintly indicated in them. They are traversed 
by numerous basic veins, from diabases to peridotites, and all 
anterior to the Torridon Sandstone. These gneisses, as I have said, 
constituted the platform against which the tremendous flood of the 
Silurian displacements stopped without shaking it; but in it are 
found traces of more ancient movements, later than the basic veins, 
and prior to the Torridon Sandstone. ‘These movements it has been 
possible to study in detail, and they have yielded precious data. 
They are narrowly localised along lines or bands of small breadth, 
compared by Mr. Peach to vertical thrust planes ; along these lines, 
which sometimes follow the veins, the latter are transformed into 
hornblende schists, with a little mica and lenses of dioritic matter ; 
the peridotites pass into talcose schists. In the gneisses there is 
mica formed in lines along the direction of the movement; the new 
