CLEAVAGE OF THE ROCKS OF THE NORTH OF SCOTLAND. 
457 
the valleys and lakes of the Highlands follow lines which, if produced, would con- 
verge on the North of Ireland, near the points of convergence of the perpendiculars 
already described. 
It must not however be supposed that all the. great physical features of the High- 
lands are connected with the foliation of the gneiss and schists ; there have been 
many disturbing forces at work at various later periods, which have broken up the 
surface into hills and valleys with very different directions. The most important of 
these are connected with the outbursts of granite, porphyry and similar rocks, far 
more numerous than are represented on any of our maps, which have broken through 
the gneiss and schists, and deranged the regularity of their foliation. Many districts 
also may have been disturbed by agents which have not shown themselves on the 
surface ; of these, the neighbourhood of Loch Lomond is a remarkable instance. 
But as the gneiss appears to be the most ancient of the formations now visible in 
Scotland, so also the physical features connected with the foliation of the gneiss 
must be regarded as the earliest of which we can take cognizance, and we must 
refer to later periods those which appear to be independent of that phenomenon. 
Foliation different from Stratification. 
In the chapter already quoted, Mr. Darwin has combated the opinion prevailing 
among geologists “ with respect to the origin of the folia of quartz, mica, felspar 
and other minerals composing the metamorphic schists, that the constituent parts of 
each were separately deposited as sediment, and then metamorphosed*.” Neverthe- 
less that opinion still appears to hold its ground, and has been lately re-asserted in a 
publication of high authorit.y'|'. 
The remarks already made on the analogy between foliation and cleavage confirm 
Mr. Darwin’s view, that “foliation and cleavage are parts of the same process;” 
for on no other supposition can we explain the conformity between the two where 
seen in contact, and their being combined in the same arch of elevation. Now as 
cleavage is almost always transverse to the bedding and obviously a change pro- 
duced in the beds after their deposition, it follows that foliation also is distinct from 
bedding or sedimentary stratification. 
But besides the argument to be drawn from the analogy of cleavage and foliation, 
a direct comparison of these with the usual disposition of the beds in stratified rocks 
of sedimentary origin, will equally serve to distinguish true stratification from those 
phenomena. 
We have seen that the arrangement of the foliation of gneiss and schist is in large 
flattish arches, in which the dip is slight near the central axis, and gradually in- 
* Geological Observations on South America, p. 1 65 . 
t Sir C. Lyell’s Manual of Elementary Geology, London, 1851, where the arguments for the sedimentary 
origin and subsequent metamorphism of gneiss, mica schist, &c. are produced at great length, and their struc- 
ture is represented as stratification and nowise related to cleavage, pp. 467 to 481. 
3 N 2 
