216 TORRIDONIAN, ETC. OF THE ISLE OP RUM. [May I903, 



completely solidified ; so the two were drawn out together, as in 

 the common experiment of making a colour-banded glass. 



The President, after referring to the great theoretical interest 

 of the paper and to its richness in detailed observations, enquired 

 whether the direction of overthrusting in Rum (which, to judge 

 from the sections, appeared to have been towards the south-east, and 

 consequently different from that in the North-Western Highlands 

 generally) was a local phenomenon only, or was more or less regional. 

 He gathered that the Author practically accepted the view that 

 the origin of the gneissose banding, and its attendant phenomena, 

 was due to the injection and consolidation of a heterogeneous magma 

 during crust-movement. Referring to some observations of his own, 

 made during a visit to Norway in 1890, he had himself been led to 

 the opinion that, in some instances at least, the phenomena might be 

 owing to the differentiation of a single original magma cooling in 

 more or less laccolitic conditions under a creeping but irregularly- 

 moving rock-cover. The parts of the collective mass might present 

 all varieties of structure, differentiation, and injection — from those 

 in which the material remained practically homogeneous, through 

 stratiform stages and areas of more or less differentiated material 

 where affected most by the crust-movements, to the final stages 

 where the whole, practically cooled, mass became fissured and injected 

 by material, in part segregated, and in part derived from greater and 

 still unconsolidated depths below. A fine example is cut through in 

 the roadside cliffs at Vik, at the head of the Hardanger Fiord, which 

 would well repay a detailed study. 



The Atjthok thanked the speakers for their remarks. With 

 reference to Prof. Bonney's observations, more especially con- 

 cerning the banded rocks of the Cornish coast, he (the speaker) 

 had understood that the structures there were attributed in the 

 main to the deformation of solid rock-masses. He fully agreed 

 with Prof. Bonney in holding that the dissolution and absorption 

 of an earlier igneous rock by a later igneous magma had often been 

 facilitated by the circumstance that the former was still hot, or 

 even not wholly consolidated, when invaded by the latter. 



In reply to the President, he said that, in Rum as in Sutherland, 

 the direction of the Mid-Palaeozoic crust-movements was from 

 south-east to north-west. The much feebler Tertiary disturbances 

 were indicated by brecciation, and probably by folding, but he was 

 not able to decide from which quarter the thrust at that epoch 

 was directed. 



