132 
Proceedings of the Royal Irish Academy. 
XXIII. — On the Geological Age awd Miceoscopic STRXJCTimE of the 
Serpentine Marble or Ophite of Skte."^ By Professors "W. King, 
Sc.D., and T. H. Eowney, Ph. D. (With plate xiv., Science). 
[Read 14t]i January, 1871.] 
FIRST PART. 
While on a tour in tlie months of June and July of the past year, one 
of us visited a portion of the Western Highlands and the adjacent 
islands of Scotland, when the opportunity was embraced of making an 
examination of the Kilbride district of Strath, in Skye. Although 
the geology of the part examined has been to a considerable extent 
described by Dr. Maccullochf and Mr. Archibald GeikieJ — by the 
latter especially — several questions have of late years arisen that render 
the present paper not altogether unnecessary. 
The district referred to, which is situated on the east side of 
Lough Slappin, between Torrin on the north, and Glen Suishnish on 
the south, consists of rocks belonging to the two great classes. § 
The principal igneous rock appears like a protruded mass, which, 
on the shore, is about half a mile in width ; while inland, and stretching 
eastward for a few miles, it constitutes the rather elevated ridge, called 
Beinn-an-Dubhaich. Both on its north side, at the promontory near 
Torrin, and on its south side near Camus Smalaig, the igneous mass 
is flanked by saccharoid calcitic marble in rudely stratified beds, 
which dip away from it at a high angle. These are overlaid by a suc- 
cession of normal sedimentary deposits, with, as the distance increases, 
a gradual decreasing inclination. 
The igneous rock, usually considered a syenite, is somewhat 
variable in mineral composition ; but in general it is crystalline 
throughout, and composed essentially of felspar (of two kinds — a pale 
flesh-coloured orthoclase, and apparently a white albite) and quartz, 
in about equal proportions, with a comparatively small amount of 
amphibole (hornblende). The rock, on account of the small proportion 
of the last mineral, cannot be considered a typical syenite. We quite 
agree, however, with Geikie, in ''ranking it among the granites." 
The marble is white, more or less crystalline — sometimes com- 
pact and waxy ; and containing here and there grains, strings, nests, 
layers, and irregular lumps, of serpentine, and other mineral silicates, 
that give it the character of ophite. Some of the additional substances 
* A paper by the authors was read at the Liverpool meeting of the British 
Association, entitled, " On some points in the Geology of Strath, in Skye." A 
considerable portion of it is included in the first part of the present memoir, while 
the subject of the second part is differently treated to what it was in the Liverpool 
paper ; and several new points are added. 
t "The Western Highlands of Scotland," vol. i., pp. 262-419. 
X "Quarterly Journal of the Geological Society," vol. xiv., pp. 1—36, 1857. 
§ See Section in Plate xiv., fig.l. 
