14 J. A, PHILLIPS ON CONCEETIONAET PATCKES AND 



On comparing the foregoing analyses with those made of corre- 

 sponding Cornish specimens (p. 8) it will be observed that the 

 proportion of ferrons oxide as compared with ferric oxide is larger 

 in the latter than in the former case. This, perhaps, in some 

 measure arises from the black mica in the Peterhead granites being 

 Haughtonite, a highly ferruginous mineral, in which the iron is 

 mainly in the state of protoxide, and which Professor Heddle has 

 shown to be present in many of the Scotch granites. 



The only exception to the rounded form of inclusion observed in 

 this district was found in a quarry at Black Hills, and is repre- 

 sented two thirds natural size in fig. 7, PI. I. 



Under the microscope this specimen is seen to be composed of a 

 mixture of dark brown or black mica with granular quartz and 

 an occasional crystal of felspar, the laminae of the mica being so 

 arranged as to produce foliation. A small quantity of magnetite or 

 ilmeuite is also present. In all rocks in which the mica in hand- 

 specimens appears black, its colour in thin sections varies from brown 

 to greyish brown. 



Near the lighthouse at Buchan Ness this granite is traversed by a 

 large dyke of micaceous f elsite, which, in places, becomes porphyritic 

 by enclosing crystals of quartz and orthoclase. 



The granite of the Ardshiel quarries situated atBallachulish, about 

 ten miles south-east of Port William, consists essentially of a fine- 

 grained mixture of quartz, nearly colourless felspar, and dark mica, 

 very closely resembling in general character the granites of the 

 Mourne Mountains in Ireland. Under the microscope this rock is 

 found, in addition to the minerals above enumerated, to contain 

 hornblende, magnetite, sphene, and apatite ; it is further observed 

 that both orthoclase and a triclinic felspar are present. 



This granite contains numerous inclusions which are often darker 

 in colour than the enclosing rock, and frequently angular or sub- 

 angular in form. Some of these have evidently the same general 

 constitution as the enclosing granite, while others are manifestly 

 enclosed fragments of foliated rocks. Ten thin sections of as many 

 different inclusions from this locality were examined under the 

 microscope with the following results : — 



The non -foliated crystalline inclusions, some of which exhibit 

 sharply defined angular outlines, were, without exception, fine- 

 grained granites precisely resembling the enclosing rock in all 

 respects, except in being finer in grain, in dark mica and hornblende 

 being more abundant, and perhaps also in a somewhat larger pro- 

 portion of triclinic felspar being present. 



The enclosures exhibiting a decidedly schistose structure vary 

 considerably in composition, and have obviously been derived from 

 rocks differing both from one another and from the surrounding 

 granite. 



Such specimens are sometimes composed of granular quartz, a few 

 fragmentary crystals of felspar, greenish-brown or nearly black mica, 

 a little hornblende, occasional small garnets, and a little magnetite. 

 In other cases hornblende and mica constitute a considerable pro- 



