1892.] Mineralogy and Petrography. 411* 



tals of arfvedsonite, biotite and an occasional diopside, imbedded in a 

 fine-grained mosaic of orthoclase and amphibole. This rock als.. eon* 

 tains spheroidal masses of orthoclase crystals that may be pseudo- 

 morphs after leucite. The dyke rocks cutting the eleolite-svenit.- are 

 grouped into eleolite-syenite pegmatites, ae-nite tinguaites ami elenlue 

 porphyries. The tinguites are non-eleolitic, while the eleolite porphy- 

 ries contain large rounded eleolites and aegiritea encloied in a tlmdal 

 mass of needles of the last-named mineral. The auntie dykes are 

 much more common in this region than elsewhere. They belong to 

 the monchiquites and the amphibole varieties of this rock. The -round 

 mass of the latter consists of a transparent mass, partly isotropic and 

 partly doubly refracting, in consequence of the development in it of 

 plagioclase and orthoclase laths. Contact rocks are rare, but in one 

 idiomorphic crystals of astrophyllite and aegirine were observed. 



The Magnet Cove region is especially interesting, not only became 

 of the fine minerals that occur there, but also because of the great 

 variety of rare rocks found in the neighborhood in great quantity. It 

 is to these latter that the minerals owe their origin. Of the eleolite-syen- 

 ite occurring here three types are distinguished. One is an eleolite 

 mica syenite, a coarse-grained rock in which eleolite has almost com- 

 pletely replaced orthoclase as the alkaline component. Eleolite-. ft] at::--. 

 schorlomites and protovermiculites measuring as much as eight inches 

 in diameter are frequently found imbedded in the decomposed rock. The 

 principal constituents of the fresh rock are alkHrionKWph* 

 tite crystals, idiomorphic zonal melanites, allotriomorphic schorlomites 

 and large round masses of the same mineral, diopside. cry.tab of ^.hene. 

 of ilmenite and of magnetite (the latter giving rise to the lodestone 

 from which the Cove takes its name), pyrite and apatite in large crys- 

 tals and in needles radiately grouped. Besides these there are also 

 found in the decomposed rock ozarkite, protovermiculite, cancrimte 

 and eaieite. The second variety of the syenite is an eleolite garnet 

 syenite made up of a granular mixture of eleolil 

 side, with small quantities of biotite and the usual accessories ine 

 third type is a miarohtic variety too much weathered to yield good 

 sections. Of the eleolitic dyke rocks one is hypidiomorphically gran- 



1 tl t idency to the trachvtic structure. It contains a large 

 quantity of orthoclase, eleolite in idiomorphic and allotriomorphic 

 "grains, large idiomorphic crystals of aegirine, cancrinite that appears 

 ' ' e in part primary, several other accessories and a number ot sec- 

 . i^___._ . k;„v. m .,vhA mentioned aegirine, fluonte 



ondary substances, among which may be mention, 

 and calcite. A pegmatitic dyke i 



nicroline crystals, 



