1857.] GEIKIE — -SKYE. 17 



each other. The greenstone-dyke extends from the road at Loch 

 Kilchrist in a south-easterly direction for fully half-a-mile, cutting 

 through marble and syenite. Along both edges of the syenite- 

 belt there are numerous smaller basalt-veins cut off abruptly, toge- 

 ther with the marble which they intersect. Similar appearances 

 are visible on the south front of Beinn na Cailleaich, where all 

 the basalt-dykes of the Sithean valley are truncated by the syenite, 

 while a large one of greenstone, traversing perpendicularly the bare 

 slope of the mountain, forms a prominent dark scar. These facts 

 seem to me to show that the trap- dykes are of two ages ; those of 

 basalt being older than the disruptive syenites, those of greenstone 

 later. The intrusive syenites are not traversed by basalt-veins, but 

 they are intimately connected with the greenstones ; and this relation, 

 when examined, throws important light upon the respective ages of 

 the different igneous rocks of the district. 



Reference has been already made to the headland of Cam Nath- 

 rach, that divides Lochs Slapin and Eishort (fig. 4). It is formed 

 by a great sheet of augitic greenstone, surmounted by an irregular 

 bed of fine-grained felspathic syenite. The greenstone, which re- 

 sembles in texture and mode of occurrence the other rocks of the 

 same kind in the district, forms a bed of considerable regularity, and 

 is connected at its southern edge with a thick dyke that cuts verti- 

 cally the nearly horizontal shales of Suishnish. The syenite, owing 

 to its liability to decay, has a somewhat irregular surface ; but it 

 undoubtedly forms a bed, and is everywhere found resting on the 

 greenstone. At the large loch on the top of the headland it has 

 carried up a considerable fragment of the calcareous sandstone of 

 Suishnish Point, and there can be no question that both greenstone 

 and syenite are alike intrusive. 



Along the eastern base of Beinn na Cham there are also at several 

 points indications of a substratum of greenstone. The same fact is 

 observable in the Hill of Harripool : that eminence forms a long 

 ridge extending southwards from the village of Harripool and merging 

 into the northern projection of Beinn na Cham. At its seaward end 

 it consists of limestones and shales belonging to the Breakish-series ; 

 and, about two miles south from the sea, beds of syenite, probably 

 ramifications of the main mass east of the Black Lochs, are found 

 intercalated with the liassic strata : at several points the syenite has 

 a distinct capping of greenstone, perhaps the result of a difference in 

 cooling, but more probably the product of a different eruption. 



The connexion of these intrusive syenites with the greenstones is 

 such as to leave no doubt that they are both later than the dis- 

 ruptive masses ; that in truth they must be regarded as the latest of 

 the igneous products of Strath. Thus the greenstones, whether 

 regarded as merely the result of a difference in cooling, or as the 

 products of distinct eruptions, confirm the conclusion that the 

 syenites are of two ages, and indicate with tolerable distinctness to 

 which class the higher antiquity should be assigned. 



It may be well, ere passing on, briefly to sum up the evidence here 



VOL. XIV. PART I. C 



