10 



GEOLOGICAL MEMOIRS. 



internal structure and mineral contents ; since the former of these 

 varieties was seldom found to contain extraneous minerals, whereas 

 the latter was generally rich in such. 



With regard to the first of these classes, reference can be made to 

 the paper itself, with its illustrations *, from which it would appear 

 that this granite shows itself in veins of all sizes, cutting through, or 

 imbedding itself in, the gneiss, and generally possessing a much finer 

 grain and more confused development than the other variety. 



The second class is treated more in detail, as being particularly 

 favourable to the development of extraneous minerals. The first 

 symptoms of the appearance of such granite seem to be where there 

 is seen here and there in the crystalline schists small nodules of 

 white quartz, of reddish-grey orthoklase, or of yellowish-white oligo- 

 klase, of a greater size than the particles composing the rock itself. 



Still further developed, as can be seen at Gronholmen, Flougsta- 

 doen, &c., these nodules are composed of one or both species of fel- 

 spar, along with quartz and mica, in particles varying in bulk up to 

 the size of the fist ; the laminae of the gneiss bend round the nodules, 

 like the woody fibre surrounding a knot in timber. 



When the size of these nodules increased, it was found that the 

 particles of their constituent minerals also became larger, less inter- 

 mixed with each other, and of better crystalline development ; and 

 further, that extraneous minerals were found more frequently present 

 in proportion to such increase of size. 



The appearances presented by such granitic masses, with their 

 progressive development, will be better seen from a few of the illus- 

 trations which are here subjoined. 



Fig. 1 is a horizontal plan of part of an irregular granitic mass in 



Fig. 1 . — Ground-plan of a granitic mass, ivith quartz-nodules, in 



gneiss at Kalvesund. 



the gneiss at Kalvesund. Lenticular masses of quartz (a, a) are 

 here seen surrounded by a mixture of orthoklase and mica. 



At Flougstadoen also is seen a similar case (fig. 2), where a 

 nodule of quartz (« «) is surrounded by a mixture of the same com- 



* In Plate III., Norske Mag. f. N. vol. viii. part 3 ; some of the figures of which 

 are here reproduced as woodcuts. — Transl. 



