CHAP. VIII 
LEWISIAN GNEISS 
117 
Hebrides is studied, we may obtain additional information regarding the 
probable origin and the earliest structures of the fundamental complex of 
the Lewisiaii gneiss. In particular, we may look for some unfoliated 
cores of a more acid character, and perhaps for evidence which will show 
that both acid and basic materials were successively protruded. We may 
even entertain a faint hope that some trace may be discovered of superficial 
or truly volcanic products connected with the bosses which recall those of 
later date and obviously eruptive nature. But up to the present time no 
indication of any such superficial accompaniments has been detected. If 
any portions of the old gneiss represent the deeper parts of columns of 
molten rock that flowed out at the surface as lava, with discharges of frag- 
mentary materials, all this superincumbent material, at least in the regions 
which have been studied in detail, had disappeared entirely before the 
deposition of the very oldest part of the Torridonian rocks, unless some 
trace of it may remain among the pebbles of the Torridonian conglomerates, 
to wdiich reference will be immediately made. 
So far, then, as the evidence noAV available allows a conclusion to be 
drawn, the Lewisian gneiss reveals to ns a primeval group of eruptive rocks 
presenting a strong resemblance to some which in later formations are con- 
nected, as underground continuations, with bedded lavas and tuffs that 
were erupted at the surface ; and although no proof has yet been obtained 
of true volcanic ejections associated with the fundamental complex, the 
I'ocks seem to be most I’cadily understood if we regard them as having 
Consolidated from igneous fusion at some depth, and we may plausibly infer 
that they may have been actually connected with the discharge of volcanic 
materials at the surface. The graphite-schists, mica-schists, and lime- 
stones of the Clairloch and Loch Carron may thus be surviving fragments 
of the stratified crust into which these xleep-seated masses were intruded, 
and through which any volcanic eruptions that were connected with them 
had to make their way. 
The limited areas occupied by the several varieties of rock in the 
fundamental complex suggests the successive protrusion ot different magmas, 
or of different portions from one gradually changing magma. Mr. Teall 
fias ascertained that whenever in this series of rooks the relative ages of 
two petrographical types can be clearly ascertained, the more basic is older 
than the more acid. 
But besides all the complexity ai ising from original diversity of area, 
structure and composition among the successive intrusions, a further 
intricacy has been produced by the subsequent terrestrial disturbances, which 
on a gigantic scale affected the north-west of Europe after the formation of 
the fundamental complex of the old gneiss, but long before the Torridonian 
period. By a series of terrestrial stresses that came as precursors of those 
which in later geological times worked such great changes among the rocks 
of the Scottish Highlands, the original bosses and sheets of the gneiss were 
compressed, plicated, fractured and rolled out, ac(j[uiring in this process a 
crumpled, foliated structure. Whether or not these disturbances were 
