346 J. J. Harris Teall — Hornblende-Bearing Hocks. 



IV. — Notes on Some Hornblende-Bearing Kocks from 

 Inchnadampf. 



By J. J. H. Teall, M.A., F.G.S. 



IN the present communication I propose to describe the petro- 

 graphical characters of some hornblende-bearing rocks which 

 occur as intrusive sheets and bosses in the limestones and quartzites 

 of the Assynt district. These rocks have been referred to under 

 various names by the different writers on the geology of the district. 

 Prof. Nicol speaks of them as gi'eenstone 1 and trap, 2 and Sir E. 

 Murchison, as syenitic greenstone. 3 Mr. Hudleston 4 indicates their 

 character more definitely by speaking of them as a " kind of diorite." 

 Prof. Bonney, in an appendix to Dr. Callaway's paper " On the 

 Newer Gneissic Bocks of the Northern Highlands," describes the 

 microscopic structure of a specimen from the Traligill Burn near 

 Inchnadampf, and designates the rock a hornblendic porphyrite. Dr. 

 Heddle 5 gives some valuable information as to the distribution of 

 the rocks, and calls attention to the perfection of form exhibited by 

 the hornblende in certain varieties. He gives a figure of the horn- 

 blende which shows the forms (110), (010) and (Oil). With regard 

 to the relations of the rocks to the associated strata he speaks some- 

 what doubtfully, but evidently inclines to the view that they are 

 intrusive. That this is the case seems proved by the absence of 

 vesicular structure and associated tuffs, and by the fact that although 

 they keep as a rule parallel with the bedding, cases occasionally 

 occur in which they can be seen to move from one horizon to another. 



Mr. Hudleston has remarked on the fact that the igneous sheets 

 have been involved in the earth-movements which have folded and 

 faulted the stratified rocks, so that the date of intrusion must lie 

 between the formation of the limestones and the production of the 

 earth-movements which have produced such striking effects in this 

 district. 



The specimens on which the following observations are based were 

 mainly collected by myself during the years 1883 and 1884. I am, 

 however, indebted to Prof. Judd for the loan of some which he 

 collected. Those collected by myself were partly obtained from the 

 limestone and partly from the quartzite. Those from the limestone 

 came from the bed which is so well exposed in the Stronchrubie 

 escarpment about three-quarters of a mile south of Inchnadampf, 

 and from the low ground to the north of Inchnadampf, where the 

 rock is exposed in many places. Those from the quartzite came from 

 two localities ; one at a point where the 500-feet contour-line crosses 

 the southernmost of two small burns which run into the Calda Burn 

 (Alt a Chalda Mdr) near the most southerly portion of its course, 

 and the other near the base of Beinn an Fhurain, rather more than a 

 mile E.S.E. of Inchnadampf. Prof. Judd's specimens came from the 

 neighbourhood of Inchnadampf, and from a point on the Allt nan 



1 QJ.G.S. 1856, p. 25. 2 Ibid. 1860, p. 97. 3 Ibid. 1859, p. 220. 

 1 Geol. Mag. 1882, p. 392. 5 Mineralogical Magazine, 1883, p. 138. 



