162 Messrs. Hicks and Davies— 
stituent here and there are suggestive of bands, but these are not 
frequent nor continuous; and these are the only indications which 
are here present as to a possible tendency to a gneissic structure. 
The micaceous constituent in these rocks does not resemble in 
any way the muscovite and biotite of the undoubted gneisses, nor, 
with the exception of 4, does it occur similarly disposed. It is 
greenish, soft, and talc-like, and is probably hydrated and bears a 
considerable resemblance to ripidolite.—T.D. 
Two special types may be described therefore of these igneous 
rocks as warranted by Mr. Davies’s careful notes, viz. granitic and 
dioritic (called granite and syenite in my former paper), and it 
seems to me that the varieties further recognized owe their peculiar- 
ities to the changes these have undergone in their passage through 
other rocks. They have frequently assimilated portions of rocks 
as they passed through them, and locally are considerably changed 
in appearance and partially in composition in consequence. 
It is clear from the following remarks by Murchison and 
Geikie' that this changed appearance as they penetrated the 
various strata was also frequently recognized by them :—“ In Glen 
Cruchalie (Glen Laggan) the most marked rock is one similar to 
that which was described as overlying the limestone at Loch-na-Fad, 
and underlying the quartz-rock at the mouth of the Hassac and along 
the higher part of the valley of Loch Maree. It is difficult to give 
this rock any one specific name, for like that in Sutherland, which 
we formerly described, it varies greatly in mineral composition, even 
within a few yards. Near the limestone it is a serpentine, the green 
mineral then thins away, and quartz and felspar take its place, 
while to these is occasionally added hornblende. The proportions 
of the ingredients also vary to a large extent. This rock, by what- 
ever name we designate it, occupies a large part of Glen Cruchalie. 
Sometimes it lies only along the bottom of the glen; then it rises 
high on the one side and soon ascends among the slopes on the 
other. In some places it occupies indifferently the place of the 
limestone, in other parts that of the quartz-rock or the upper flaggy 
series, or it invades the three zones at once.” 
Prof. Nicol describes the intrusions near the head of Loch 
Maree and at Glen Laggan as follows:*—“A great mass of 
igneous rock, a fine-grained syenite, or rather diorite, forms the 
base of the hill (head of Loch Maree), covered by broken masses 
of quartzite and limestone. In the valley of the Laggan the 
limestone has been quarried in several places, dipping to H. 20° S., 
but much altered by the diorite, which forms a wide mass, running 
for several miles along the valley.” The above remarks might 
lead one to think there was but one recognized type amongst these 
intrusions, and that the differences recognizable were due every- 
where to accidental circumstances. I noticed, however, at once 
that we had here to deal with at least two types of intrusive rocks, 
probably entirely independent of one another, and of different age; 
1 Quait. Journ. Geol. Soc. vol. xvii. pp. 190 and 192. 
* Quart. Journ. Geol. Soc. vol. xvii. p. 103. 
