J. J. Harris Teall — Hornblende-Bearing Bocks. 349 



of the view that this mineral was a product of the consolidation of 

 the original magma. 



Apatite. — This mineral occurs in the form of limpid hexagonal 

 crystals, which are usually four or five times longer than broad. 



Magnetite. — A small amount of original magnetite occurs in grains 

 and crystals. The opacite (secondary magnetite ?) which occurs 

 associated with the chlorite has already been referred to. 



Calcite occurs in the form of fine dust thickly scattered through 

 some of the more altered specimens, and also as large crystalline 

 plates in sections which contain the colourless pyroxene. It is pos- 

 sible that the portions of crystalline calcite may be fragments of the 

 limestone caught up by the igneous magma at the time of its intrusion. 



Epidote has already been referred to in describing the alteration of 

 the hornblende. It is difficult to say whether all the epidote has 

 been formed in this way. 



Quartz is present as a secondary and probably also as a primary 

 constituent in some varieties of the rock. 



Mica arises in connection with the alteration of felspar, and it is 

 sometimes found associated with ill-defined aggregates of epidote. 



Description of the Kocks. 



Macroscopic examination shows that the above minerals occur in 

 very different proportions in the different varieties of the rock. In 

 some the hornblende is very abundant, and these as a rule have a 

 granular aspect ; in others it is comparatively scarce. The latter 

 usually contain two generations of felspar and have a marked por- 

 phyritic aspect. For the purpose of description we will term them 

 hornblende porphyrites, and the former diorites. It must be remem- 

 bered, however, that the diorites tend to become porphyritic by the 

 conspicuous development of hornblende ; such varieties will be termed 

 porphyritic diorites. The diorites also present us with varieties of 

 texture depending on the coarseness of the grain. In some the con- 

 stituent minerals may be easily recognized, in others they are so 

 small as to require the microscope for their determination. The 

 latter occur in the thin sheets and at the margins of the intrusive 

 masses. 



In the porphyritic diorite near the base of Beinn an Fhurain con- 

 cretionary patches occur which are more coarsely crystalline and 

 richer in hornblende than the main mass of the rock. In these 

 patches as in the main mass an aggregate of felspar individuals plays 

 the role of ground-mass. As a rule the outlines of the inclusions are 

 smooth and curvilinear, but sometimes the large hornblende crystals 

 project for a short distance into the main mass of the rock. It is 

 clear that we have here phenomena similar to those described by Mr. 

 Phillips 1 in the case of the granites. The inclusions in the rock 

 now under consideration agree with those described by Mr. Phillips, 

 (1) in form ; (2) in being more basic in composition than the main 



1 " On Concretionary Patches and Fragments of other Rocks contained in 

 Granite," Q..J.G.S. vol. xxxvi. p. 1 ; and "Additional Note on Certain Inclusions 

 in Granite," QJ.G.S. vol. xxxviii. p. 216. 



