Vol.50.] ANNIVERSARY ADDRESS OP THE PRESIDENT. Ill 



composition (propylites), secondly the acid series, and thirdly the 

 basic series. By way of incidental confirmation of the priority in 

 time of the acid over the basic series, he read a paper, about a year 

 ago, on Inclusions of Tertiary Granite in the Gabbro of the Cuillin 

 Hills in Skye. This kind of granite in its more central parts is de- 

 scribed as a true biotite-granite, but there is a constant tendency for 

 the biotite to be replaced wholly or in part by hornblende. When the 

 quantity of plagioclase inci'eases in amount the rock passes into a 

 common granitite or hornblende-granitite. Towards the peripheral 

 portions of the intrusive masses a marked change takes place in the 

 characters of the rock, the mica and hornblende are gradually 

 replaced by augite, magnetite becomes a prominent constituent, 

 whilst a remarkable drusy structure is developed. It is this variety 

 of rock which has been called granophyre, and it passes in turn into 

 ordinary quartz-felsite. The gabbros are typical, exhibiting every 

 gradation from augite-gabbro to common or diallage-gabbro ; and 

 the monoclinic pyroxene is to a greater or less extent liable to be 

 replaced by bronzite or hypersthene. 



Prof. Judd then proceeds to describe an interesting junction of 

 granitic rock with gabbro along a ridge, some 1000 feet above sea- 

 level, on the north-east side of the far-famed Loch Coruisk. At this 

 place inclusions of the granitic rock, sometimes having an area of 

 several square yards, are found to be completely enveloped in the 

 mass of the gabbro, which here exhibits all its ordinary characters. 

 Indeed, the inclusions may be said to occur near to the line of one 

 of the largest and most typical junctions of gabbro and granite in 

 the whole region. 



Some doubt, in the course of the discussion on this paper, was 

 thrown on the actual relations of these acid fragments to the 

 encasing rock. But setting such doubts and others of a similar 

 nature aside, and admitting that the inclusions are portions of some 

 of the acid masses of the Tertiary volcanic series in the Hebrides, 

 the question arises as to whether the Author is entitled to say that 

 he has, in this way, brought forward any valid proof of the relative 

 ages of the basic and acid bosses of the "West of Scotland. Sir 

 Archibald Geikie thinks not. That geologist referred to traces of 

 acid protrusions at an early part of the volcanic history of the 

 region, and suggested that the inclusions might belong to this early 

 series of acid rocks, of which only ejected fragments had yet been 

 found. He further alluded to a remarkable portion of the junction- 

 line between the granite and the gabbro, in the same neighbourhood 



