and Igneous Rocks of Ensay. 107 



In this ground-mass are — (a) large, very cavernous augite 

 crystals, some of which are twinned in the usual manner. 

 These are of the first consolidation, but there is also a later 

 generation of augite, in well-developed short prisms, with the 



planes oo P (110)— co P oo (010)— oo Y oo (100). 



These crystals contain magnetite, and also colourless 

 granules of raagnia, arranged in concentric lines of growth. 

 The earlier augite crystals contain much fewer inclusions. 

 (b) Ehombic pyroxene, both in irregular-shaped masses and 

 prisms with rectangular terminations. This pyroxene is very 

 fibrous, in some sections roughly fibrous, of a brown colour, 

 and markedly dichroic in shades of brown and brownish 

 yellow. The absorption is c > b > a. It does not contain 

 any inclusions. It is traversed across the prism by flaws, 

 from which alteration extends on either side. The smaller 

 prismatic crystals, which may possibly be of a second genera- 

 tion, resemble the crystals of enstatite, which I have observed 

 in the Diabase porphyrite at Buchan. 



As the monoclinic and rhombic pyroxenes are about equal 

 in amount, this rock can be considered to stand midway 

 between Diabase and Norite. 



Other samples are of very light colour, with outlines 

 showing of felspar crystals. One sample I found to be 

 composed of a ground-mass of triclinic felspars. In this are 

 other triclinic felspars, as porphyritic crystals, but much 

 altered to epidote. Besides these there is a little iron ore, 

 but neither augite nor any other bisilicates. Traces of 

 viridite and very numerous small apatite prisms complete 

 the composition. 



I also examined a sample which resembled the above ; but 

 the ground-mass in this case consists of small felspars and 

 innumerable rounded granules of coloured doubly-refracting 

 material, apparently devitrified magma. In this are traces of 

 porphyritic plagioclase felspars, and also masses of epidote 

 crystals and crystalline grains,which,I think, probably replace 

 augite. These interesting rocks are also to be classed with 

 Diabase, and the two types which occur here remind one, in 

 some of their features, of those palaeozoic Diabases which 

 have received from Gtimbel the names respectively of 

 Proterobas and Leukophyr. 



The Diabase rocks which I have now briefly noted have, 

 in some respects, a strong family resemblance to the Diabase 

 porphyrites of the Buchan district, and may be thought 



