Vol. 52.] FOLIATED GRANITES IN EASTERN SUTHERLAND. 635 



same year (1890) Mr. Home obtained confirmatory evidence of the 

 ' lit par lit ' introduction of granitic materials into the crystalline 

 schists south-west of Strath Halladale. In the autumn of 1891 and 

 1892 Mr. Home surveyed the coast-section between Kirktoniy and 

 Armadale and the tract extending south-eastward iowards the 

 Armadale burn, where there is a group of complex gneisses formed 

 by alternating folia of granitoid materials and granulitic or coarsely 

 granulitic gneisses or schists, recalling some of the Lewisian types 

 between Cape Wrath and Laxford. These phenomena, which seem 

 to have been developed at a later date than granulitic schists of the 

 ' Moine ' type, were briefly summarized in the Annual Report of 

 the Geological Survey for 1892. 



From the northern coast of Sutherland these intrusive granite- 

 masses and pegmatites have been traced across the county by 

 Forsinard, Kinbrace, and Kildonan to the Ord, Helmsdale, and Upper 

 Strath Brora: Mr. Greenly having mapped the Embrace and 

 Kildonan area, and our late colleague, Mr. Hugh Miller, the tract 

 between the Ord and Upper Strath Brora. During 1893-94 Mr. Hugh 

 Miller observed the phenomena resulting from the minute penetra- 

 tion of the eastern schists by granite on an extensive scale in the 

 outlying parts of Rogart and Clyne. His observations in Upper 

 Strath Brora led him to the following conclusions. The structures 

 in the granites and granitic gneisses were supposed by him to be 

 1 to a large extent imitation-structures, due to a simulation of the 

 form and structural features of the country rock (the eastern 

 schist) by granites that have by some means crept into their place. 

 The process by which this replacement has been effected seems to 

 have been a development of crystalline matter among the granulitic 

 materials of the pre-existing schists and quartzites. In the earlier 

 stages of metamorphism the granitic substance has entered or by 

 some means suffused the structure of the stone, appearing first as a 

 fine mottling of granitic particles. In further stages of meta- 

 « morphism the granitic matter, keeping for the most part to the folia 

 of the pre-existing rock, has increased into knots and knotty 

 strings, has entered planes, slide-planes, and the lines of contortion 

 in the contorted schists, and so thickens into bands and sills at the 

 expense of the original rock, till the latter is represented only by 

 inclusion- planes and ultimately by inclusion-structures. The 

 crystalline matter of the granitic gneisses and granites remains 

 optically complete, and the inclusion-structures and the inclusion- 

 planes everywhere retain the same dip and strike as that of the 

 country rock, not only in Upper Strath Brora, but also in Rogart and 

 wherever present in the granite massifs of Helmsdale and the Ord 

 of Caithness. Parts of these granites are in fact pseudomorphs or 

 granite-casts preserving as replacement- structures remains of the 

 structure of the pre-existing rock.' 



Q. J. G. S. No. 208. 2 x 



