6 J". A. PHILLIPS ON CONCRETIOITAIIY PATCHES AND 



present. The crystals of orthoclase often enclose grains of quartz 

 and patches of a triclinic felspar. 



Six different sections were prepared of as many dark micaceous 

 inclusions from this locality, and, with the exception of two, they 

 were found, when examined under the microscope, to differ from 

 one another in the fineness of their grain only. Four of the speci- 

 mens consist essentially of a mixture of granular quartz with felspar, 

 through which numerous flakes of dark mica are disseminated. 



The felspar does not very often exhibit any traces of triclinic 

 striation ; but the plates of mica are usually arranged with their 

 axes approximately parallel to the same plane. As is almost 

 invariably the case in this locality, the inclusions are much closer 

 in grain than the granite, and the quartz, which is found chiefly 

 in patches, occurs mostly in granules from '75 millim. to 1 millim. 

 in diameter. In addition to the foregoing constituents, these patches 

 enclose minute and imperfectly crystallized garnets of a dark- green, 

 colour, magnetite, or ilmenite, and imperfect crystals of tourmaline. 

 The larger crystals of garnet are sometimes -5 millim. in diameter, 

 while the smaller ones are frequently made up of an aggregation of 

 exceedingly minute blebs separated from one another by spaces 

 filled up with quartz. 



The two remaining sections of inclusions from this locality differ 

 from the preceding only in containing a less proportion of felspar, 

 the absence of which is compensated for by the presence of a large 

 quantity of a bacillar colourless mineral, which is probably tremolite. 



At Wicca Pool, Zennor, granite in the form of veins penetrates 

 for a considerable distance into the mica-slates forming the sea-cliff, 

 and fragments of slate which have been detached from the general 

 mass have become enclosed in the granite. These enclosed fragments 

 are angular, their outlines are sharply defined, and their union with 

 the surrounding granite along the surfaces of contact is complete. 



In general appearance the included fragments can scarcely be 

 distinguished from specimens of the general mass of the micaceous 

 rock taken from along the line of its direct contact with the in- 

 trusive granite, excepting that foliation has been almost obliterated. 

 Sections of the mica-slate in contact with the granite are seen under 

 the microscope to consist of a mixture of granular quartz, brown 

 mica, and a little white mica — the last being present in very small 

 quantity only, with a few occasional minute garnets and a 

 considerable amount of magnetite in the form of disseminated 

 grains. 



Thin sections prepared from fragments found by Mr. H. Bauerman 

 enclosed within the granite do not differ materially from those made 

 from contact specimens, excepting that both the quartz and mica 

 are in this case more distinctly crystalline. 



When seen in polarized light, sections cut from the included 

 fragments and those from the slate in immediate contact with the 

 granite veins are scarcely to be distinguished from one another, as 

 the grains of quartz in the contact-specimens then become well 

 defined; their average diameter, from '07 millim. to •! millim., is 

 the same in both instances. 



