302 REV. J. F. BLAKE ON THE 
conglomerate is quite independent of it, and forms a massive which 
must be studied by itself. Further collateral proofs will be derived 
from the manner in which this massive holds together as a whole, 
not only in this immediate district but elsewhere. 
The existence of tuffs above the conglomerate appears to me 
quite a secondary matter in the question; there might, or might 
not, be such tuffs without seriously affecting the independence of 
the lower series, as there are certainly tuffs on higher horizons. 
Nevertheless, neither the specimens collected, nor the sections said 
to show inosculation that have been indicated, nor the diagrams of 
the microscopic slides given in Dr. Geikie’s paper yield satisfactory 
proofs of identity in character between any beds above and any 
beds below the conglomerate. 
We have next to consider the more interesting question as to the 
true character of these rocks. Are they sedimentary or are they 
igneous? On this subject I feel that any arguments of mine will 
have more weight with myself than with any one else ; but to me they 
are overwhelming in favour of the essentially igneous origin of the 
whole (including, of course, ashes and volcanic mud as igneous rocks). 
First, with regard to the rock considered to be granite by some, and a 
metamorphosed aqueous rock by others: I believe we are learning 
from an improved stratigraphy to be more cautious in regarding many 
rocks as the metamorphosed representatives of what we are also 
acquainted with in their unmetamorphosed state: but whether meta- 
morphosed or not, there is no reason why a primitive granitic rock 
should not be stratified in structure, even if not sedimentary, 
according to the ordinary sense, in origin. But such stratification 
is not to be proved by planes of division, which, however constant. 
in direction, may well be joint planes, but by differences in mineral 
character along definite bands, either on a large or on a small scale. 
It is true that such bands of a partly calcareous nature have been 
indicated by Dr. Hicks at Porthlisky Point; but these have not. 
been brought prominently forward, as they should have been, if 
without any doubt they had the significance assigned to them; and 
though unable to find such myself, I think it prebable they are 
correctly explained by Dr. Geikie. But elsewhere I could trace 
no such bands, In the Bryn-y-garn quarries there are varieties of 
texture; but these do not run in bands, and the finer-grained masses 
have more the appearance of irregular veins. The microscopic 
structure of both forms is nearly identical. In the coarser the quartz 
has crystallized before the felspar ; but in the finer the felspar has. 
sometimes crystallized first; and sometimes the two have gone 
together, producing that micropegmatitic structure which Mr. Davies 
has noted in the rock from Porthlisky, and which is not uncommon 
in undoubtedly igneous granites. In both, the third constituent is 
the same chloritic mineral, more frequently in radiating lines occu- 
 pying narrow interstices, but occasionally in complete and inde- 
pendent crystals, The structure of the rock at Porthclais is essen-. 
tially the same. Here and there are inosculations of the two 
minerals, and both are occasionally characterized by abundance of 
