686 L. V. FIRS SON 



analcite in the rocks investigated by him, Lindgren was forced 

 to conclude from the very fresh and unaltered character of the 

 material that it must be of primary origin. The examination of 

 the Highwood rocks by the author confirms this view of Lind- 

 gren's. Anyone who has seen the fresh unaltered character of 

 the minerals in these rocks, not only from Montana but from 

 Brazil and from other localities, would find it difficult to explain 

 how the base could have undergone a thorough chemical change 

 and decomposition throughout without the other minerals being 

 affected in the slightest degree and especially the olivine, of all 

 minerals perhaps the one most delicately susceptible to processes 

 of hydration. It actually appears that henceforth we must 

 accept analcite as an important and common rock -forming 

 mineral, almost unquestionably one may say of primary origin. 

 It is understood of course that its occurrence as a secondary 

 mineral also, is not for a moment denied or its importance 

 underrated. It must be said, however, in view of the facts now 

 presented, that many cases where it has been called a secondary 

 mineral are at least doubtful. Many authors for example cite it 

 as secondary after leucite, and one gathers the impression from 

 the context that this is supposed to have happened by weather- 

 ing ; though how leucite, which is a potash compound, is to 

 change into analcite, a soda compound, by the simple addition 

 of water, is not stated. It is true that Lemberg has shown that 

 leucite is changed into analcite by the action of soda solutions ; 

 but, as in the case of the monchiquites, it can hardly be sup- 

 posed that such an action could have taken place without alter- 

 ing the other minerals, and it would be difificult to see where so 

 great a quantity of soda, as would be required, could have come 

 from. It is also difificult to see how it could have formed from 

 nephelite, norian or sodalite without the formation of other sec- 

 ondary products as noted above. 



Lindo^ren' suo^g-ests that the mineral could have formed from 

 igneous magmas, provided that the magma contained water and 

 crystallized under sufficient pressure to retain it, and cites the 



^Op. cit., p. 52. 



