114 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1894, 



from the granite, as for instance where grits are highly altered and 

 shales but little affected. This certainly is just the reverse of what 

 we should expect, unless the word ' grit ' in this case implies some- 

 thing more than an assemblage of quartz-grains. She was, on the 

 whole, disposed to believe that the variation in the amount of altera- 

 tion at the same distances, the mode of alteration of the grits, and 

 the transference of material might be accounted for by the passage 

 of highly heated waters, and it was to the action of these that she 

 mainly attributed the contact effect. It is just possible that this 

 view may receive some countenance from the observation of Prof. 

 Brbgger that the chemical nature of the intrusive rock does, in 

 certain cases, produce an influence on the character of the meta- 

 morphism. It is not easy to perceive how this could happen other- 

 wise than through the convection of solvents. Mr. Barrow believes 

 that Miss Gardiner's investigations have an important bearing on 

 the origin of the crystallization of the Highland schists. 



We have now to consider two papers, contributed by officers of 

 the Survey, dealing with the subject of certain igneous rocks in the 

 schists of the Highland border. The first of these, by Messrs. Dakyns 

 and Teall, on the Plutonic Rocks of Garabal Hill and Meall Breac, 

 is devoted to the description of some rocks which occur in a complex 

 forming a belt of high ground almost immediately to the west of 

 the lower end of Glenfalloch, on the confines of the counties of 

 Perth, Argyll, and Dumbarton. These rocks are stated to vary 

 considerably in chemical andmineralogical composition, and, although 

 gradual passages are found between more or less acid varieties, in 

 other cases the junction is sharply defined. The more acid are 

 always found to cut through the less acid rocks, when the two are 

 found in juxtaposition, and the fragments occurring in a rock are 

 observed to be less acid than the rock itself. Although thus shown 

 to be of different ages, they must clearly be referred to one geological 

 period. This period was not defined by the Authors, but, to judge 

 from the remarks of Mr. Barrow, the igneous mass is probably older 

 than the Old Red Conglomerate, yet more recent than the general 

 metamorphism of the Central Highlands. Basic rocks, mainly of the 

 diorite type, but containing two notable bodies of peridotite, form a 

 sort of fringe on the south-east side of the mass, which is, in this 

 direction, considerably mixed up with the country schist owing to 

 faulting ; next comes an area of tonalite and non-porphyritic granite, 

 and lastly, on the west side, a relatively large area of porphyritic 

 granite of ordinary structure ; in one locality only a gneissose struc- 

 ture may be observed, the planes of foliation curving round included 



