BY H. I. JENSEN. 537 



biotite, and becomes also somewhat schistose in appearance. The 

 gneiss becomes poorer in quartz near the line of junction, and its 

 minerals become corroded and resorbed, giving place to many of 

 the syenite minerals. It appears therefore that the intruded 

 mass has been strongly attacked by the intrusive. 



Since in the primeval basins one would expect limestones pre- 

 cipitated with alkaline salts, it is fair to ask if, in view of 

 Hogbom's proof as to the origin of the limestone, we may not 

 consider the foyaite too the result of the refusion of alkaline beds 

 by basic intruded masses. 



3. Serra d" Monchique Rocks of Portugal.* — The alkaline rocks 

 cover an area of 60 square kilometers, and comprise many varieties 

 of nepheline-syenite, foyaite, pulaskite, etc., and in the border 

 zone sanidinite. Dykes of tinguaite, bostonite porphyry, nephe- 

 line syenite porphyry, camptonitic tinguaite, monchiquite, and 

 camptonite are represented. At Picota occurs a leucite-tinguaite 

 vitrophyre. The basic group comprises nepheline tephrite, nephe- 

 line basanite, amphibole-monchiquite, and amphibole-biotite- 

 camptonite, fourchite and ouachitite. 



Of rare minerals lavenite is mentioned, and also moiree micro- 

 cline and analcite secondary after leucite. Near the contact the 

 intrusive rocks become fine-grained and dense. 



In the foyaites and pulaskites interesting masses of basic rock 

 frequently occur which Kraatzlan and Hackmann describe as due 

 to contact with the slates. It seems to me that these may admit 

 of a different explanation (cf. basic inclusions in orthoclase basalt, 

 W.67, Warrumbungle Mountains, and in the monchiquitic 1am- 

 prophyre, N.18, Nandewar Mountains). 



The contact-effects of the monchique mass on the greywacke 

 and Culm slates prove it to be later than early Carboniferous. 

 The mass is situated on a north and south line, an anticlinal 



• E. Kaleszinsky's Report in Neues Jahrbuch fur Mineralogi B.B. iii. 

 1884; and "The Nepheline Syenites of Sierra de Monchique " by K. von 

 Kraatzlan and V. Hackmann, Tschermak's Min. u. Pet. Mitth. xvi. 1896, 

 pp. 197-307. 



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