CORRELATION WITH FOREIGN ROCKS. 20g 



Whilst the American anorthosites and norites resemble the 

 basic members of the charnockite series in their 

 Norites of Scandinavia, mineralogy, a much more striking analogy can 

 be found in Norway, where Vogt 1 has de- 

 scribed a group of hypersthenic rocks in which the basic varieties 

 are associated with an acid form composed of potash-felspar, quartz, 

 rhombic pyroxene and a small amount of plagioclase, thus resem- 

 bling most perfectly our charnockite (c /, p. 134). What makes the 

 analogy more complete in all these cases is the similarity of the 

 mineralogical habit, so to speak, of the chemical compound ; thus 

 we never find sphene in the unaltered members of the charnockite 

 series, but the titanic oxide always seems to be in the form of 

 ilmenite, and this is true also of the rocks described by Vogt, 

 These rocks have recently been more fully described by C. F. 

 Kolderup in the Ekersund and Soggendal areas. The types repre- 

 sented vary from the ultra-basic ilmenitite, through pyroxenites, 

 norites, labradorite rocks, monzonites, banatites and adamellites to a 

 bronzite-granite. The resemblance of these to our Madras rocks 

 which was indicated by Vogt's brief description of them, is brought 

 out more strikingly by Kolderup's details, and by his direct com- 

 parison with specimens from Madras. 



Reviewing the whole evidence, we must conclude that we are not 

 yet in possession of sufficient facts to define the precise difference 

 between these old norites and the pyroxene-granulites. Most probably 

 they were originally similar formations, which, on account of second- 

 ary changes induced in the presumably older pyroxene-granulites, are 

 now distinguishable by differences more easily recognised than de- 

 scribed. However, the one important point to be considered by us at 

 present is that between the norites which are certainly eruptive and 

 the pyroxene-granulites whose origin is doubtful there are so many 

 points of resemblance still left that we have good prima facie 

 reasons for expecting evidences which will show that the two groups 

 of rocks are really similar in origin. 



1 Zeitschr. fur. prakt. Geol. t 1893, p, 4. 



( 91 ) 



