The Scottish Naturalist. 133 



morphic rocks have been forced over the underlying sedimentary 

 and unaltered deposits. 



1 1. Much of the Eastern Gneiss is merely the Archaean * gneiss 

 repeated ; the Logan rock of the Assynt district is generally the 

 Archaean 2 brought up from below the sedimentaries, and the Arna- 

 boll rock of Eriboll 3 is a part of the same Archaean (Hebridean) 

 gneiss. 



THE METAMORPHISM. 



12. The penological, lithological, and mineralogical distinctions 

 between the Hebridean gneiss and the Logan 4 and Arnaboll 

 Rocks and their equivalents are primarily due to the extraordinary 

 mechanical disturbances 5 to which the latter have been subjected. 



1 3. The planes of schistosity in the Eastern Metamorphic schists, 

 &c, between and above the great fault-planes, are not planes of 

 bedding ; 6 they are planes of shearing and cleavage, gliding planes 

 (thrust-planes) along which the rocks have yielded to the lateral 

 crust-pressure. 



14. By the agency of this lateral earth-thrust, the Archaean, the 

 plutonic, and included patches of sedimentary rocks have been 

 locally sheared and flattened out into rocks resembling halle 

 flintas 7 and rhyolites, even finely-laminated shales. 



15. This Eastern Metamorphic series of Sutherland and Ross 

 not only contains Archaean rocks, but also local patches of metamor- 

 phosed Palaeozoic, 8 intrusive, and segregatory rocks, together with 

 local patches of material probably compounded of all these in 

 different degrees. 9 



16. This Eastern Metamorphic series has received its present 

 strike pseudo-bedding and its present foliated and mineralogical 

 characteristics through the agency of the crust movements which 

 have operated within the district since Lower Silurian times. 10 



Some of these conclusions may appear startling at first sight to 

 these who have not followed with interest and appreciation the 



1 Nicol QJ.G.S., 1861, p. 95, Hicks, QJ.G.S., 1S78, p. 818, &c, &c., 

 a Bonney, Huddleston, Proc. Geol. Assoc, 1879, p. 75, QJ.G.S., 1880, p. 

 95 ; Callaway, ibid., 1883, p. 410. 



3 Lapworth, QJ.G.S. , 1883, p. 422, &c. 



4 Compare Bonney, QJ.G.S., 1880, p. 95, &c. 



5 Lapworth, 1884, see Appendix, p. 103. . 



b Lapworth, 1884, I.e. Compare also Bonney, QJ.G.S. ^ 1883, p. 415, i\:c< 



7 Lapworth, I.e. 1884. 



8 Compare Hicks, 1883, QJ.G.S., p. 147. 



9 Lapworth, 1884, ibid., p. 104. 



10 Lapworth, 1884, ibid., p. 105. 



