Vol. 50.] ANNIVERSARY ADDRESS OF THE PRESIDENT. 113 



activity in these ancient sedimentary systems must have been com- 

 paratively local. In the area lying to the west of the post-Cambrian 

 movements these igneous rocks extend over a distance of about 9 

 miles from north to south, but in the region affected by those 

 movements the distance is stated to be 24 miles. Originally they 

 must have penetrated far to the eastward, for they are carried in a 

 westerly direction with the associated sedimentary strata along the 

 higher thrust-planes, indicating that the period of activity to which 

 they belong is later than the Cambrian limestone of Durness and 

 earlier than the post-Cambrian movements. 



With few exceptions the rocks intrusive in the limestones are 

 more basic than those in the quartzites, although hornblende-bearing 

 rocks are common to both series. The Loch Borolan porphyry is 

 described as an intrusive mass; the greater poition is highly 

 granitoid, the prevalent type in the west being a coarse granitic 

 rock consisting maiuly of orthoclase with a little quartz, occasionally 

 porphyritic with some mica ; the second type, east of Loch Borolan, 

 is characterized by dark garnets associated with orthoclase and a 

 blue mineral, and may be foliated or non-foliated. This, I presume, 

 is the rock described as ' Borolanite,' a group especially characterized 

 by the association of orthoclase and melanite, and which naturally 

 falls into the elaeolite-syenite group, though in this case melanite is 

 raised to the rauk of an essential constituent. The action of the 

 various intrusive masses and especially of the Loch Borolan porphyry 

 upon the limestones is highly interesting ; whilst the evidence of 

 their physical relations to each other is brought forward in such a 

 way as to leave little doubt that recognizable bands of Durness 

 limestone have been converted into marble such as that of Ledbeg 

 by contact with the eruptive rock. 



It would be interesting to follow this subject further, more 

 especially when one remembers what has been written about the 

 Ledbeg marbles and the curious rocks associated with them, but 

 the claims of other papers must be recognized, and there are yet 

 three on Scottish matters, two of them relating more or less to the 

 subject of contact-metamorphism. Taking these in the order of 

 their appearance, the first is by Miss Gardiner on contact-alteration 

 near New Galloway. It is, in the main, a microscopic paper and 

 relates the changes produced in an alternating series of grits and shales 

 towards the north-east of a granite-mass known as the Cairnsmore 

 of Fleet. The Author notices the extreme variation in the degree 

 of alteration undergone in different places at the same distance 



