MR J. HORNE AND MR J. J. H. TEALL ON BOROLANITE. 169 



immediate contact with the marble. An excellent section of the igneous rock is exposed 

 in a small tributary of the Ledbeg River, showing the intrusive mass penetrating the 

 marble. The altered limestone can be traced from the northern limit of this igneous rock 

 for a distance of about 150 yards to the base of Ben Fuarain, where it is covered by 

 crushed Torridon sandstone. Here again a gradual passage is observable from the white 

 crystalline marble into the white limestone of the Eilean Dubh group. The crushed and 

 shattered Torridon sandstone, overlying the marble and unaltered Durness limestone, 

 rests unconformably on Lewisian gneiss, and both are covered in turn by the basal 

 quartzites and a small portion of the " Pipe-Rock." All these materials, viz., the gneiss, 

 the Torridon sandstone and Cambrian quartzites, are separated from the underlying 

 limestone by a complete discordance. They form one of the most interesting of the 

 numerous outliers of displaced materials resting above the Ben More thrust-plane. 



Proceeding to the south-west slope of Sgonnan Mor, several sections of special interest 

 are met with, revealing the relations of the igneous mass to the surrounding strata. On 

 this declivity four small streams unite to form an important tributary of the Ledbeg 

 River at Luban Croma. In each of these burns the intrusive rock is visible, and in the 

 two most northerly there are excellent sections showing peculiar types of the igneous 

 mass penetrating the marble between the 1000 feet and 1250 feet contour lines. Not far 

 above this level, both the marble and the intrusive rock are abruptly truncated by the 

 Ben More thrust-plane bringing forward a slice of Archaean rocks covered unconformably 

 by the Torridon sandstone and Cambrian strata. On the south-west slope of this 

 mountain, the Torridon flags, shales and grits overlie in inverted order the igneous rock 

 and the marble, for as we ascend the slope the strata have a persistent easterly dip till 

 we reach the coarse conglomerate at the base of the Torridon sandstone, in contact with 

 the overlying Lewisian gneiss and its basic dykes. 



The ground between Sgonnan Mor and Kinloch Ailsh has not been surveyed in 

 detail, but from certain traverses across the area it seems apparent that the intrusive 

 igneous rocks reappear at certain localities with the displaced materials overlying the Ben 

 More thrust-plane. 



In the neighbourhood of Strath sheaskich near Loch Ailsh the eastern limit of the 

 intrusive mass can be approximately defined by means of rocky knolls projecting through 

 the peat and drift. It is bounded by massive white marble, apparently resting on the 

 igneous rock, and dipping towards the east at angles varying from 30° to 70°. This 

 junction line can be traced through the gap, close by the Kinloch Ailsh road to the 

 high road leading to Inchnadamff. 



The southern limit of this great intrusive mass is to a large extent obscured by the 

 extensive covering of peat stretching continuously from the Kinloch Ailsh road westwards 

 to Loch Urigill and Ledmore. But occasional exposures of rock are to be found in the 

 streams cutting through the peat and drift. It extends far to the south of the road 

 between Loch Borolan and Aultivullin, for it is visible in small burn sections about three- 

 quarters of a mile due south of Aultivullin. Here again it is overlapped by the Cambrian 



