164 MR J. HORNE AND MR J. J. H. TEALL ON BOROLANITE. 



Again, in 1859, Murchison called attention to a band of syenitic greenstone, 

 intercalated in the grey limestones at the bend of the road about a mile west from 

 Inclmadamff. He states that it is from 40 to 50 feet thick, and as regularly bedded as 

 the limestone both above and below it, though on examination it is seen to be a true 

 igneous rock, containing crystals of hornblende with felspar and quartz. The indica- 

 tions of contact alteration produced by this igneous mass had evidently attracted his 

 attention, for he notes that the limestone above the igneous rock is more altered than 

 that which lies beneath it, being in parts a crystalline marble.* 



In his brief summary of the igneous rocks of Sutherland, in the same communication, 

 Murchison refers to an igneous rock of felspathic character, with some varieties, which, 

 though termed porphyries, are rather syenites, breaking through the quartz-rocks far 

 above the limestone of Assynt. These rocks spread out into large masses in the tract 

 to the east of Assynt, which is traversed by the road to Oykel Bridget 



In 1860, Professor Nicol announced that, in the course of the previous year, he had 

 observed that the Canisp porphyry not only breaks through the quartzite overlying the 

 Torridon sandstone, but forms a mass more than a mile in diameter in the quartzite 

 within a few hundred yards of the Inn at Inchnadamff. From these facts he inferred 

 that the igneous intrusions must have been later than either the red sandstone (Torridon) 

 or quartzite. J 



In 1882, Mr Huddleston referred to some of these igneous rocks in the Cambrian 

 strata of Assynt, describing them as " a kind of diorite." 



In his various papers published in the Mineralogical Magazine from 1881 to 1884, 

 Professor Heddle gave the results of his detailed examination of these rocks. He 

 indicates the distribution of the Canisp porphyry, and speaks of it as one of the 

 most striking porphyries of Scotland. He describes it as a structureless paste of a buff 

 or dull brown colour, studded with crystals of a bright brick-red colour, commingled with 

 others of a pale yellow ochre tint and with minuter ones of a dark green. He notes the 

 occurrence of porphyritic crystals of orthoclase with albite and augite in the rock.§ 

 Regarding the igneous rocks in the quartzites and dolomite in the neighbourhood of 

 Inchnadamff, he refers to their distribution, and points out some of the lithological 

 varieties, from the Canisp porphyry to the more basic types found in the limestone, in 

 which hornblende is more abundant. IT Special reference is made to the remarkable 

 " red porphyry " of Loch Borolan, and to the large area which it occupies from Ledbeg 

 eastwards towards Kinlochailsh.** He takes exception to the name given to the rock of 

 this hilly region, because no true porphyritic structure can be seen in it ; it has two 

 ingredients, felspar and quartz, the former showing traces of crystalline form while the 

 latter is frequently altogether absent. He defines the rock as a mass of agglutinated 

 granules of a more or less brilliant red felspar. While indicating the localities of the 



* Q. J. G. Soc, vol. xvi. p. 221. § Min. Mag., vol. iv. p. 233 et seq. 



t Q. J. <1. Soc, vol. xvi. p. 232. T Min. Mag., vol. v. pp. 136 to 144. 



I Q. J. G. Soc, vol. xvii. p. 99. ** Min. Mag., vol. v. p. 144 and p. 295 et seq. 



