THE MITAMOBFmC ROCKS OF ADELIE LAND STILLWELL. 95 



hornblende schists, which seem to become part of the Fundamental Complex, and where 

 intrusive junctions are only occasionally met with, biotite gneisses and hornblende 

 gneisses are characteristically developed. Hence the obvious nature of the dyke masses 

 at Cape Gray, their less obvious appearance at Cape Denison, and their partial 

 destruction at Cape Denison, are matched by similar instances in the Scottish area. 

 Remarkable variation in mineral and structural composition is noted in both areas, 

 and the dominant types are the same in both cases. 



The above remark of Home illustrates the incomplete separation of the second 

 and third groups from the Fundamental Complex, and it also appears to be evidence 

 of the development of biotite gneisses and hornblende gneisses in the same way as at 

 Cape Denison, viz., by the destruction of the walls of the basic dykes by metamorphic 

 diffusion. 



In some cases, as in the Gruinard district (p. 176), it is clearly shown that the 

 basic dykes form an absolutely different series to that which supplied the early basic 

 material in the Fundamental Complex. On the other hand, in the description of 

 the Cape Wrath to Laxford area (p. 107), it is recorded that the grey biotite gneiss, the 

 hornblende biotite gneiss, and the dark gneiss alternate in bands and areas of 

 varying breadth, having no sharply defined boundaries, but graduating from the more 

 acid to the more basic types. These types cannot be distinguished on the field map, 

 and are therefore considered only as portions of the primary mass. In the description 

 of the Loch Maree to Gairloch area (p. 195) it is recorded that field distinction is 

 impossible between the hornblende gneisses with quartz and hornblende gneisses 

 without quartz on account of their variation. These last two cases afford further 

 analogy to the Cape Denison rocks, where hornblende gneisses are considered to 

 be metamorphic products of a mixture of grey gneiss and amphibolite, resulting from 

 metamorphic diffusion. 



Thus it is a perfectly natural result that it should be recorded in the Loch Maree 

 and Gairloch district (p. 195) that the " early basic rocks " (those which have not 

 been separated from the Fundamental Complex) are more variable in composition than 

 the basic dykes. The basic dykes, which happen to be parallel to the direction of 

 foliation, are only recognised as such when they have escaped metamorphic diffusion, 

 and a varying amount of diffusion will produce varying results. In the Loch Carron to 

 Point Sleat (Skye) district the rocks are stated (p. 262) to consist of biotite and horn- 

 blende gneisses with bands of hornblende schist, which are considered to represent the 

 basic dykes in the unmodified areas of Lewisian gneiss in Ross and Sutherland. Had 

 these bands been dislocated, and had they then suffered metamorphic diffusion, they 

 would certainly present the same features as the " early basic rocks." I do not argue 

 that there is but one series of pre-Torridonian basic dykes in the North- West Highlands 

 to which both the so-called " early basic " and the " basic " rocks may be referred. 

 There are at least two, and possibly more, but I do mean that the " early basic " rocks 



