acapemy op sciences] NORTHERN EUROPE. 15 



to the effect of movements during crystallization. These relations are clearly the reverse of 

 those which the hypothesis of gravitative differentiation in situ would lead one to expect. 



In Mull the complexity of the record is increased by the repetition of the cycle of igneous 

 activity, but as the publication of the detailed account of this region is expected before long, no ■ 

 summary will here be given of the progress-reports that have been issued. 7 



The features in Arran and Carlingford do not call for special mention in this place. The 

 latter is classical for the evidence therein of the relation of granophyre to quartz-gabbro. 

 (Sollas '94.) 



FINLAND AND SCANDINAVIA. 



The basic rocks of this area are mostly of pre-Cambrian or early Palaeozoic age. The 

 former are very abundant, but can not be discussed fully as yet from a tectonico-petrographic 

 standpoint. The later pre-Cambrian (Jotnian) rocks of Finland are invaded by differentiated 

 laccolites, sometimes gravitationally arranged, at times showing hybrids allied to the marscoite 

 of Skye. Occasionally the gabbroid rocks are associated with granites. Many of the occur- 

 rences of gabbro and peridotite in this Jotnian complex have a marked stratiform arrangement 

 suggestive of intrusion during folding (Sederholm '03). 



The Caledonian period of crust-folding produced huge overthrusting with which was 

 associated the development of the great masses of basic igneous rocks of Norway, consisting of 

 gabbro, rich in titanium, norite, anorthosite, and peridotite. These have a stratiform appear- 

 ance, as noted by Vogt ('02) and Kolderup ('03). With these basic rocks are associated mon- 

 zonitic granites and syenites, which become notably sodic in the Bergen region, an association 

 which seems an extension of a feature already noted in the presence of kentellanites with the 

 Caledonian basic rocks of Scotland. The order of intrusion of these plutonic rocks in Norway 

 is not always from basic to acid but sometimes intermediate, basic, acid (Hogbom '13). 



Goldschmidt ('16) has summarized and extended the studies of these rocks in southern 

 Norway. They are referable to three series or "stems." That of the green lavas and intrusive 

 rocks is comparable with the series of Ordovician igneous rocks of Scotland and the pietre verdi. 

 It consists of tuffs, variolitic spilites and diabases (associated with radiolarian jasper) paleopi- 

 crite, and sills and laccolites of gabbro, periodotite and pyroxenite. The igneous activity 

 extended from late Ordovician times into the period of Caledonian orogeny, for dynamically 

 metamorphosed gabbros lie concordantly in the planes of schistosity of the invaded formations. 

 These rocks have a normal calcic composition except for a rather sodic diabase, the analysis 

 of which is cited by Falkenberg ('14). The occurrence of sulphide-ores in connection with the 

 gabbros of this stem has long been studied by Vogt and others. 



The opdalite-trondhjemite stem is probably cognate with these. It contains as its earliest 

 members pyroxenite and peridotite, but only as large inclusions in dynamically altered gabbros 

 and norites, and also diorites and trondhjemite (asodicgrano-diorite). The rocks form steeply 

 inclined laccolitic masses concordant with the schistosity of the invaded formations. They 

 were erupted after the rocks of the first-mentioned stem, but before the conclusion of the Cale- 

 donian orogeny, and were exposed to erosion in Devonian times. "It is quite probable that 

 ■b geological connection exists here between the orogeny and the plutonic intrusion." The 

 rocks are comparable with the later plutonic rocks of Scotland, the East Alpine tonalites, etc., 

 and the American granodioritic series. 



The stem of the Bergen-Jotun rocks is probably, but not clearly, related to these two stems. 

 It has been studied chiefly by Kolderup ('03, '11, '14, '15), who showed its affinity to the charn- 

 ockite-anorthosite group of Rosenbusch. It comprises peridotites and pyroxenites in small 

 lenticular or rounded masses inclosed in the gabbros and orthoclase-bearing norites. With 

 these are labradorite-rocks with cataclastic structure, in which a single dike of peridotite has 

 been recorded. The latest members of the stem are hypersthene-syenites and alkaline granites. 

 The close association between the intrusion of these rocks and orogenic movement is shown by 



' The writer had the privilege of studying Carrock Fell and Skye with field directions given by Dr. Barker, and of examining part of Mull In 

 company with Dr. Thomas and other officers oV the Geologieal Survey then investigating the island. 



