Alfred Harher — Igneous Rocks of Skyc. 507 



British Isles to beyond the Arctic Circle. The episodes of the 

 Local Series, on the other hand, were closely related to certain 

 special foci of activity, declared at a very early epoch, one of 

 which was situated beneath what is now the mountain district of 

 Central Skye. While events of the two classes often alternated in 

 our area, and are integral parts of one complete record, they may 

 be regarded as in some degree independent and as bound up with 

 two distinct orders of crust-movements, viz. the continent-building 

 and the mountain-building respectively. Of the two parallel series 

 of eruptions, the Eegional retained throughout a basic character, 

 while the Local developed wide petrographical differences among 

 the several groups. It follows that the successive episodes of the 

 Eegional Series are much more difficult to separate and arrange in 

 order than those of the Local Series, and the following condensed 

 scheme is confessedly imperfect, especially as regards the basic lavas 

 and the basic dykes. 



(0) Pre-Volcanic Phase : Local Series. — Here may be noticed 

 certain plutouic intrusions nowhere exposed at the surface and 

 known only from fragments in the volcanic aggloraei-ates. They 

 are confined to the central mountain district, and include, in order, 

 (a) gabbro and (h) granite. 



(1) Volcanic Phase. — Regional activity almost continuous; local 

 chiefly confined to two well-marked episodes. 



Eegional Series. — Fissure-eruptions of basic (with some sub-basic) 

 lavas throughout the region. Besides the prevalent olivine-basalts, 

 there are some hypersthene-basalts, augite-andesites, etc., but no 

 ordered sequence has been made out. 



Local Series. — Central, not fissure-eruptions. 



(a) Paroxysmal outbursts at certain centres, marked by great 

 accumulations of volcanic agglomerate ; the large vents confined to 

 the mountain district. The chief masses of agglomerate underlie 

 all the lavas, and thus represent the earliest overt manifestation of 

 igneous activity. 



(b) Eruptions, only in part paroxysmal, of intermediate and acid 

 rocks in one limited area on the northern border of the Cuillins. 

 Generalized sequence : (i) trachytes, (ii) rhyolitic tuffs and breccias, 

 (iii) rhyolites. This group is intercalated as a local episode in the 

 midst of the basic lavas. 



(2) Plutonic Phase. — Eegional activity in abeyance ; local at 

 maximum of intensity and at the same time narrowly localized. 



Local Series. — Plutonic intrusions in the forms of complex 

 laccolitic masses and bosses. Three groups, in order of increasing 

 acidity, with little or no intervals. 



(a) Peridotites of the south-west Cuillins; viz., olivine-anorthite 

 rocks, picrites, and typical peridotites, including duuite. 



(b) Gabbros of the Cuillins, etc. 



(c) Granites and granophyres (plutonic) of the Red Hills. 



(2 to 3) Transitional Phase, Local Series only.— The phase of 

 Minor Intrusions shows, as compared with the Plutonic, a reversal 

 of order among the groups of local intrusions. There seems to have 



