THE PROBLEM OF THE ANORTHOSITES 231 



site. Not impossibly, then, there may be in the Morin area a 

 stratified mass, made up of syenite above and anorthosite below, 

 with general relations similar to those we have imagined to exist in 

 the Adirondacks. 



Lack of miner alizers in the Morin anorthosite. — On an earlier 

 page it was pointed out that there is in anorthosite no supply of 

 minerals other than plagioclase adequate to produce significant 

 lowering of the melting temperature of the plagioclase. Anortho- 

 site could exist as magma, therefore, only at very high temperatures 

 unless there was present a proportion of volatile components suf- 

 ficient to produce great lowering. Adam's work on the Morin 

 anorthosite appears to give a definite negative answer to this 

 possibility. The minerals normal to the anorthosite are those 

 commonly believed to form from relatively anhydrous melts. The 

 ferromagnesian material appears typically as pyroxene, not as horn- 

 blende or mica. There is little if any tendency for the pyroxene to 

 be made over into hornblende or mica even in the very latest stages 

 of crystallization when the volatile components would reach their 

 maximum concentration. Even intense shearing of the rock, 

 which took place partly during this latest stage of crystallization 

 and partly immediately subsequent thereto, had no tendency to 

 develop hornblende and mica from the pyroxene, though under 

 such conditions it is well known to be particularly susceptible to 

 this change if there are mineralizers present in significant quantity. 



All of the evidence points to a substantial lack of mineralizers. 

 The Morin anorthosite is in these, as in most respects, typical of 

 the world's anorthosites. We are therefore impelled toward the 

 belief that, inasmuch as anorthosites show no definite high- 

 temperature characters, they are preferably to be considered as 

 never having been molten as such. 



Anorthosites as small intrusions. — In considering the physical 

 condition of the anorthosite as bearing on this question of its origin 

 it is perhaps well to recall the circumstances under which Adams' 

 investigation was undertaken. Prior thereto there had been a 

 common tendency to believe that all banded rocks were of sedi- 

 mentary origin, and since the anorthosite is often markedly banded 

 it had been regarded as a member of the sedimentary series with 



