No. 7.] APATITE IN NORWAY. 439' 



proved that veins of similar mineralogical composition may occur 

 in entirely different sorts of rocks (vide supra) .* 



Our apatite-bearing veins are of eruptive origin.. We shall 

 first discuss a point which would seem to oppose their eruptive 

 origin. In many deposits, some of them being the principal 

 ones, there occurs, as already mentioned, a symmetrical arrange- 

 ment of the vein-minerals. Thus, for instance, in the Oedegar- 

 den veins brown phlogopite and sometimes also crystals of green 

 enstatite, in many hornblende-deposits hornblende, and in several 

 apatite-bearing enstatite veins enstatite occupies the sides of the 

 veins, while their centre consists of apatite and very often also 

 of other minerals. This banded arrangement might seem per- 

 haps to indicate a regular gradual deposition of the minerals out 

 of watery solutions. Frequent exceptions, however, occur even in 

 the most regular deposits ; wherein no such systematic arrange- 

 ment is observed. Sometimes, the vein minerals throughout the 

 entire extent of the veins are mixed with one another equally 

 and without arrangement, at other times the veins do not contain 

 the same minerals in their different portions. In veins that consist 

 chiefly of a single mineral, apatite and other minerals are often dis- 

 tributed equally through the entire vein mass. The symmetrical 

 structure of our veins can, with regard to regularity, be in no 

 way compared to that which is so splendidly displayed in many 

 metallic veins. 



We explain the banded arrangement of the minerals in our 

 apatite veins by the assumption that under favourable conditions 

 the minerals that now occur on the sides of the veins (usually 

 hornblende or mica) were first crystallised out of the magma 

 under pressure. 



The veins exhibit also the phenomenon so often observed in 

 eruptive veins, that the vein-minerals are fine-grained on the 

 wails next the country-rock, while in the centre of the veins they 

 have formed larger crystals. 



In the Oedegarden veins, moreover, the fine scales of mica 

 near the walls are sprinkled with small grains of apatite. Both 

 minerals must therefore have crystallised out together, before 

 the large crystals of mica that project into the apatite, and finally 

 the central apatite itself was formed out of the still liquid vein 



* Limestone occurs very seldom as a rock, so far as we know, in 

 the entire region where the apatite-hearing veins occur. 



