1857.] GEIKIE — SKYE. 11 



of the Middle series, were thrown down, enveloping the remains of 

 Ammonites Jamesoni, A. brevispina, and A. Davozi. The circum- 

 stance is interesting, therefore, in a twofold point of view : 1st, 

 because it proves that the disturbing agencies which afterwards 

 played such an important part in Hebridean geology had already 

 begun to show themselves as early as the time of the Lower Lias ; 

 and, 2ndly, because it clearly indicates that in the same ancient 

 period the forces which produced the parallelism of the Scottish 

 glens and mountain -chains acted in the prevailing north-easterly 

 direction. 



Igneous Rocks. — The igneous rocks of Strath belong to two great 

 classes, and assume three distinct modes of occurrence. There are, 

 first, the various hills and mountain- chains of syenite — huge amor- 

 phous masses breaking through and overlying the liassic beds ; and, 

 secondly, the innumerable dykes of augitic trap that cut the strata 

 at every angle, and not unfrequently spread out between them in a 

 bedded form. 



The northern limit of the liassic region was described as formed by 

 a bold eruption of syenite rising into an elevated chain of mountains 

 (see Map, PL I. fig. 1). The summits of these hills, bleak and bare, 

 rise out of a thick mantle of shattered blocks and broken debris, 

 which, together with the scantiness of the vegetation, give them an air 

 of ruin and desolation. Beinn na Cailleaich, the highest of the range, 

 attains an elevation of over 2000 feet. In addition to this great 

 syenitic tract, there are numerous minor isolated portions scattered 

 throughout the district. Of these the largest is Beinn an Dubhaich, 

 which stretches eastward from the shore of Loch Slapin for about 

 three miles, with an average breadth of about a quarter of a mile. 

 Another syenitic hill of considerable size is Beinn na Cham, rising 

 abruptly above the hamlets and cultivated patches of Borereg. It 

 is of an irregular form, thickest towards the west, and tapering to a 

 point in the opposite direction. The Hill of Harripool may be re- 

 garded as a continuation of Beinn na Cham. It runs as a long 

 sloping ridge in the direction of the village from which it derives 

 its name. The rocky headland named Cam Nathrach, that forms 

 the point of Suishnish, is likewise a syenitic protrusion, having an 

 irregularly oval form, and bulging out a little towards the west, like 

 the other detached eminences. There is but one other portion of 

 considerable size in the district, — the rounded hill, called Ben 

 Bhuidhe, that rises over the western arm of Broadford Bay. 



In addition to these, however, there occur numerous smaller erup- 

 tive masses in various parts of Strath. One juts over the rugged 

 path along the cliffs of Loch Slapin, between Glen Kilbride and Glen 

 Suishnish ; another projects into the breccia between Loch Lonachan 

 and Beinn na Charn. I have observed several more, and it is pro- 

 bable that others may have escaped my notice. Indeed, after a 

 somewhat lengthened examination of the district, the conviction 

 forced itself upon me that there might be large masses of syenite 

 hidden at no great depth beneath the surface, especially in the more 



