14 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 22, 



an illustrative example. This hill forms the elevated promontory 

 between Broadford Bay and the Sound of Scalpa, and occupies an 

 area of not much less than a square mile. The coast-line is fringed 

 with low flat reefs of black shale, identical with that of Pabba ; and 

 as the waves have in many places cut a steep cliff that topples over 

 the beach, the connexion of the igneous rock with the lias-beds can be 

 accurately studied. Nothing could present a greater contrast to the 

 junction of the syenite and marble along the flanks of Beinn Dhearg 

 or Beinn an Dubhaich, than the junction of syenite and shale along 

 this sea-margin of Beinn Bhuidhe. Here we see no great tilting of 

 the beds, no wide-spread metamorphism, no wall-like contact of the 

 two rocks. On the contrary, the shales dip gently under the sea, 

 showing in many places no evidence of their proximity to a large mass 

 of igneous rock. They are unaltered except within a foot or there- 

 abouts from the syenite, and at the contact show a flinty porcelain- 

 like texture. The syenite has manifestly rolled over them, catching 

 up fragments in its progress, insinuating itself, after the manner of 

 the traps, into cracks and fissures, and conforming exactly to all the 

 inequalities of the stratification. Fig. 8 shows the manner in which 

 this junction is displayed along the cliff-section. 



The Junction of Syenite and Shale at Beinn Bhuidhe (fig. 8). — 

 Here the syenite is a lighter-coloured, more felspathic, and finer- 

 grained rock than that already described. At the point of contact 

 it is very homogeneous and compact, and hand-specimens may easily 

 be obtained showing the two rocks fused together — an appearance 

 nowhere observable among the disruptive syenites. 



The headland of Cam Nathrach must be referred to the same 

 overlying class with Beinn Bhuidhe. Its structure is represented in 



The overlying nature of Beinn na Charn is well displayed along 

 its eastern boundary, where the limestones and shales dip under 

 it, unaltered save near the point of contact ; and there, it may be 

 remarked, they are not by any means so much changed as near 

 the disruptive masses ; nor is the limestone in any instance altered 

 into a white crystalline marble, as it is along the northern hills. 



The Hill of Harripool is more complex in its structure, and not 

 less manifestly a superjacent, intrusive mass (see fig. 3). At its 

 northern extremity it subdivides, shales and limestones being found 

 between the separated portions. In truth, it is identical in its mode 

 of occurrence with an ordinary greenstone, which it further resembles 

 in the limited amount of its attendant metamorphism. 



Such, then, being the marked differences between these two forms 

 of syenite, I think the inference may be legitimately drawn, even 

 were there no other evidence, that they are not probably the 

 products of contemporaneous eruptions. At Beinn Bhuidhe they 

 approach within a few hundred yards of each other, and it is incon- 

 ceivable how at the one spot the rock should have tilted up, pierced, 

 and greatly metamorphosed the strata, after the manner of the granite 



