256 PETROLOGICAL ABSTRACTS AND REVIEWS 



Crazy Mountains. As a matter of fact, they were first found some 

 years later by Wolff in Costa Rica, While in his first published descrip- 

 tion Rosenbusch does not make the predominance of the dark constituent 

 a necessary qualification, in his later works he grouped the theralites and 

 shonkinites, and said of them: "Die Theralithe und Shonkinite sind 

 hypidiomorphkornige Tiefengesteine, welche bei starker Vorherrschaft 

 der dunklen Gemengtheile durch die Mineralcombination Nephelin mit 

 Kalknatronfeldspath, bezw. Nephelin mit Kalifeldspath, charakterisirt 

 sind," consequently there can be no light theralites. The analyses of 

 various theralites are recast into both the C.I.P.W. and Osann's system. 

 The ijolite is described fully and analyzed. It dififers from the usual 

 ijolites in the presence of arfvedsonite-hornblende. The modal per- 

 centages determined by the Rosiwal method are: nephelite 38.25 

 per cent, arfvedsonite-hornblende 31.96 per cent, aegirite-augite 16.24 

 per cent, titanite 5.78 per cent, mosandrite 3.81 per cent, magnetite 

 2.37 per cent, apatite 1.59 per cent. The rock, consequently, may be 

 classified as 3126 (new form, or 3 131 old form) of the reviewer's system. 

 The chemical analysis of the rock is computed in the C.I.P.W. system as 

 Ivaaros, and is compared with three other ijolites, one a Malignos, one an 

 Ivaaros, and one an Ijolos. In an appendix are given analyses of fifty- 

 four theralites and related rocks. 



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