546 OGILVIE 



THE PERFEMANES. 



Dunose. V. i. i. i. (Dunite). Occurrence. — This rock was 

 found in a single exposure, close to the cross roads where the 

 road from Bayville to Pleasant Cove intersects that from East 

 Boothbay to Boothbay Harbor. The exposure was not large: 

 the rock disappeared on the one hand under a vegetable garden, 

 on the other it was cut off by the highway. The occurrence was 

 apparently a dike. 



Petrological Character. — In the hand specimen the rock was 

 dense, black with green talcose spots, and fine textured. It 

 proved on microscopic examination to be somewhat altered, but 

 its origin could so clearly be seen that it is placed in the new 

 system of classification. 



Microscopically it was found to be mainly olivine. This is 

 evidently of a very magnesic variety, magnetite and chromite 

 enough being visible to use up all the iron shown in the analysis. 

 There is present a small amount of an alteration product which 

 has the strong double refraction, high interference colors, and 

 low index of refraction characteristic of a carbonate. From the 

 analysis it is evident that it must be magnesite, no lime being 

 present. A little muscovite and a little chlorite are present. 

 The green spots which were in evidence megascopically are 

 found to consist of fibrous anthophyllite with a few small areas 

 of opaline quartz. A few rosettes of serpentine are also to 

 be seen. 



These alteration products occupy relatively small areas and 

 invariably occur either along the cracks of the olivine or else they 

 retain the form of the olivine. It is evident that the original 

 rock was pure olivine of the variety forsterite, with small 

 amounts of magnetite and chromite. Fully three fourths of 

 the areas of the slides are now occupied by these original minerals, 

 and since the alteration products retain the olivine form, the 

 inference is safe that no lime can have been lost in the alteration 

 process. There is a little mica which may possibly be original. 

 No feldspar or pyroxene is or has been there. 



