Vol. 50.] ACID ROCKS OF THE IXNER HEBRIDES. 217 



are the alternations of a dark, fine-grained, massive rock, which 

 under the microscope shows a gabbro-like structure, with remarkably 

 banded and much coarser varieties of gabbro. These varieties of 

 rock follow each other in rude beds, which run in a general N.N.W. 

 direction. I shall on another occasion describe in more detail the 

 remarkable structures of the banded gabbros, which have a suggestive 

 bearing upon the origin of the structures in some of our oldest 

 gneisses. 1 It maybe sufficient to state here that the banded sheets, 

 as well as those of finer material with which they are intercalated, 

 have a general easterly dip, but sometimes curve round so as to incline 

 towards S.S.E., the angle of dip being usually above 20° (see fig. 1, 

 p. 222). The remarkable segregation of the component minerals of 

 these banded sheets into lenticular laminae gives them a strikingly 

 gneiss-like aspect (PI. XIII.). This structure continues up to the 

 very edge of the granophyre, where it is abruptly truncated. 



These rudely bedded and banded gabbros are traversed by veins 

 and sills of a remarkably coarse and massive form of gabbro. 

 Another abundant variety consists of pale, more felspathic material, 

 which, taking the form of veins and strings, traverses all the other 

 gabbros. These pale veins obviously belong to the gabbro series, 

 to which, under the microscope, their affinity is abundantly clear. 

 They are the ' white veins ' referred to by Prof. Judd in his post- 

 script as easily distinguishable from apophyses of a granite. Put 

 they are not the veins described by me as proceeding from the 

 granite (or granophyre) at this locality. 



One of the most remarkable constituents of the gabbro ridge is a 

 large mass of coarse agglomerate, which forms a group of knolls and 

 crags among the gabbros, its eastern margin being truncated by the 

 tolerably straight boundary of the granophyre. It contains abundant 

 blocks of various slaggy lavas like those of the basalt-plateaux. 2 

 Dykes of fine basaltic material intersect the agglomerate and the 

 gabbros. 



1 In various papers Prof. Judd has repeatedly asserted that I'went so far 

 wrong in my work among the volcanic rocks of the Western Isles as to mistake 

 the gabbros for Laurentian gneiss. My error never went further than a 

 suggestion, which, however, 1 thought at the time probable. The suggestion 

 was made in a very guarded way in a footnote on p. 210 of the first edition of 

 my ' Scenery of Scotland,' published in 1865 : — ' If the hypersthene rock of the 

 Cuillin Hills of Skye belongs to this ancient formation' [Laurentian gneiss]. I 

 had never had an opportunity of carefully studying the rock, and therefore never 

 described it in any of my writings. But I had in my early years in Skye crossed 

 some parts of it, and had been astonished by its gneiss-like aspect. Any geo- 

 logist who is familiar with the Lewisian gneiss, and sees for the first time the 

 banded gabbros of the Cuillin Hills, will readily appreciate how I should have 

 been led from only cursory examination to connect the gabbro with metamorphic 

 rocks. The publication of Prof. Zirkel's paper in 1871 (Zeitschr. Deuts^h. geol. 

 Gesellsch. vol. xxiii. p. 1) — that is, three years before Prof. Judd entered the 

 ground — completely satisfied me that the gabbros were part of the Tertiary 

 volcanic series. 



2 There are probably many scattered masses of agglomerate among the Cuillin 

 Hills, which will be found when the ground is mapped in detail. There must 

 be at least one in the basin of Harta Corry, and a mass of the rock occurs at 

 the head of Corry na Creiche. 



Q.J.G.S. .No. 198. <i 



