Reviews — /. M. Sohral — Nordingra, east coast Sweden. 87 



this area, but the discussion of their relations to the gabbros and 

 granites is reserved for a future publication, which will contain 

 analyses. One development of anorthosite in Nordingra is remarkable 

 for the abundance of apatite which it contains. 



A very striking feature of the petrographical work is the care with 

 which the optical constants of many of the minerals have been 

 determined. The most interesting result of this work is the proof 

 of the occurrence of fayalite in many granitic and monzonitic rocks 

 of the region. This mineral appears to occur in several of the typical 

 granites, but it is noticeable that it becomes most prominent in those 

 rocks which are regarded as products of assimilation of gabbro or 

 anorthosite by the granites. The significance of its occurrence cannot 

 be discussed until the rocks have been analysed. 



In the two islands of Ulfon there is a large development of granite 

 intruded by diabase with associated acid and basic dj'.kes. The acid 

 dykes are in part contemporaneous with and in part younger than 

 the diabase : the)' consist of albitites and albite-pegmatites. One of 

 these has been made the type of a new rock name, Varusingite : it 

 is a coarse-grained rock consisting mainly of albite with some augite, 

 magnetite, and titanite, and is regarded as a ' diabase-pegmatite '. 

 The basalt dykes are the youngest rocks in the district. They show 

 an abnormal development of plagioclase phenocrysts in a narrow zone 

 at their contact with the diabase or granite. This is attributed to 

 inoculation of the intruding magma, when in the metastable state, 

 by the plagioclase of the country rock. 



Monzonitic rocks occur in this region and range from rather acid 

 varieties to rocks allied to kentallenites, but containing olivine rich 

 in iron. From a study of the field relations of these rocks the author 

 is led to the conclusion that they are derived by assimilation of 

 granite by the diabase. If this be the case it forms a very important 

 example of the assimilation of an acid by a more basic rock, and, 

 further, it shows that ' hybrid ' rocks are not necessarily of very 

 unusual composition. Pending the publication of more analyses 

 these conclusions will possibly be received with some hesitation. 

 Two analyses of kentallenites are given and one of a fayalite-monzonite. 

 The field relations of these occurrences are not conclusive, and the 

 occurrence of fayalite at once suggests comparison with the monzo- 

 nitic rocks of the mainland ; this point will doubtless be settled by 

 the author in his further publications. At Svartbergsviken is an 

 inclusion-like occurrence of monzonitic rocks, grading from adamellite 

 at the centre, through banatites and monzonites, to a variety of the 

 Ulfo diabase, and here the field evidence of assimilation is more 

 convincing. Two analyses of the ' hybrid ' rocks are given, together 

 with analyses of the diabase, but still more analyses are needed to 

 strengthen the case. There appears to be no close connexion between 

 the composition of the rocks of this occurrence and the kentallenites 

 and fayalite-monzonites mentioned above, and in criticizing the con- 

 clusions of the author the two groups must be considered apart. 



Petrologists will await further contributions on these rocks with 

 great interest, for none can fail to appreciate the real excellence of 

 the present work. W. C. S. 



