[alcock] NORITE ROCKS 29 



Beerbachite rocks closely resembling their type have been de- 

 scribed from Frankenstein, Odenwald in Hesse, in the gabbro of the 

 Radauthal at Harzburg, in the gabbro of the Scottish island Rum, 

 and from Monhegan island, Maine. Two analyses are given in the 

 literature of them, the first of. a beerbachite from Frankenstein given 

 by Rosenbusch, in his Gesteinlchre ; the second shows the average 

 composition of six specimens from Monhegan island.^ 



Melanocratic Type 



Hyper sthenite. — Cutting the typical norite north of the rapids on 

 Stone river immediately east of Lake Athabaska are found small 

 dykes and irregularly shaped masses of a dense dark rock, which 

 represents the lamprophyric phase of the norite. On a weathered 

 surface it has a reddish-brown shade, but a freshly broken specimen 

 shows a very dark greenish-grey appearance. It is dull in colour and 

 aphanitic. 



In thin section the rock is found to consist almost entirely of 

 orthorhombic pyroxenes; of these hypersthene is much the most 

 abundant, but a non-pleochroic variety, which is enstatite, is also 

 present in considerable quantities. Iron ore and feldspar occur as 

 accessory minerals. The former consists of magnetite, and a little 

 yellowish iron ore, which is either pyrite or pyrrhotite. The feldspar 

 consists of small fragments of labradorite between the pyroxenes. It 

 does not amount to more than, three per cent, of the rock. In texture 

 the rock is even granular, and has suffered little alteration. 



E. C. E. Lord, Amer. Geol., Vol. XXVI, 1900, p. 346. 



