TRANSACTIONS OF SECTION C. 751 



syenites, and the peculiar rock to wliich the term borolanite has teen applied. 

 These hasic border rocks are richer in lime, iron, map:nesia, and titanic acid, though 

 still containing alkali felspar and nepheline. This is proved by the occurrence of 

 biotite, segirine-augite, melauite, and sphene. 



There are three possible ways in which the complex may have originated : 

 (1) successive intrusions ; (2) differentiation iw sjfw ; and (3) modification of the 

 original magma by the absorption of material from the adjacent limestones or 

 dolomites. 



The fact that transitional forms between the main types are abundant seems 

 to suggest that successive intrusions of sharply differentiated magmas have not 

 played an important part in the building up of the complex. The formation of a 

 border facies of basic rocks, richer in lime and magnesia, can be explained by 

 absorption from the adjacent limestones or dolomites, but the enrichment in iron 

 and titanic acid, as represented by the frequent abundance of melanite and sphene, 

 cannot bo so accounted for. The evidence at present available suggests that 

 differentiation, coupled, it may be, with some absorption of material from the 

 adjacent sedimentaries, has been the main agent in forming the complex 



But, however the complex may have originated, it is certain that the magmas 

 representing the more acid and the more basic portions appear outside the plutonic 

 area as dykes and sills. Thus to the north there are felsitie rocks containin"' 

 aegirine closely allied in composition to the quartz-syenites, and in the Coigach 

 district of West Ross-shire, about seventeen miles to the west of Cuoc-na-Sroine, 

 there are dykes of borolanite. 



The main object of this communication is to call attention to the extremely 

 interesting petrographical province — unique so far as the British Islands are 

 concerned — of which Cnoc-na-Sroine forms a part, and to the problems connected 

 with it which still await solution. 



4. On a Granophyre-dyke Intrusive in the Gahhro of Ardnamurclian, 

 Scotland. By Professor K. Busz, of Milnster. 



Similar contact-phenomena to those already known of Barnavave in Ireland 

 and of Strath on the isle of Skye have been found near the village of Kilhoan 

 on Ardnamurchan, where a granophyre-dyke, intrusive in a surrounding mass of 

 gabbro, has not only eflected alterations of the gabbro, but Jxas also undergone 

 alterations in its own composition through the absorption of basic material. 



The gabbro occurs in two varieties, the one being a fine sugar-grained black 

 rock, without any macroscopically visible structure, the other showing a porphy- 

 ritic structure and containing small black crystals or crystalline ao-Teo'ates of 

 triclinic felspar. 



They both consist of anorthite, pyroxene — diallage and common augite and 



magnetite ; rhombic pyroxene in considerable quantity is also present in the por- 

 phyritic variety. 



On the junction line, where the granophyre and gabbro meet, all constituents 

 have been greatly altered. The triclinic felspar gradually passes into orthoclase 

 and the alteration-product of pyroxene is hornblende (usually uralite), brown mica, 

 and secondary granular augite. 



The granophyre consistsof quartz generally in well-defined crystals and of 

 grey orthoclase, which serves as interstitial matter. It also contains a great 

 number of rectangular felspar crystals, the centre of which in many cases consists 

 of triclinic felspar (gabbro-xenocrysts). It appears spotted with numerous black 

 patches of different size, mostly minute, which are the remains of pvroxene-xeno- 

 crysts, originated from the gabbro and showing every stage of alteration. 



The results of the examination of these rocks lead to the following conclusions; 



1. The gabbro is presumably a dyke-rock, belonging to the group- which has 

 been termed beerbachitft, and also partly a porphyritic variety of the same— 6eer6a- 

 chite-porj^hyry. 



2. It was solidified before the iatrusion of the granophyre, as the latter contains 



