20 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 19, 



stone, which forms the base of the next hill, and is well exposed, 

 both on the road and on the shore east of the town. It is seen to 

 be covered by the quartzite ; but the continuation of the section is 

 obscured by detritus, which has collected behind a rocky promontory 

 projecting into the loch. This promontory consists of a massive 

 intrusive rock, in some places a kind of syenite, or a felspar-porphyry 

 with hornblende, in others rather an impure serpentine*. In one 

 place it is covered by a bed of quartzite ; but on the shore to the 

 east the first strata seen are thin-bedded grey gneiss, dipping 17° S. 

 5° E., but the beds are often much twisted and contorted. On this 

 line, therefore, the relations of the quartzite to the gneiss are not very 

 clearly exhibited ; but that it overlies the red sandstone is beyond 

 doubt. 



The valley of the Auchal river lays open a still more instructive 

 section. The north-west side of the valley is the continuation of the 

 same range which forms the coast ; and, as shown in the section 

 (from A to b), the red sandstone distinctly dips under the white 

 quartzite forming the summit of the hill. The continuation of the 

 same beds, with the same relations, is seen on the other side of the 

 valley, followed by the road from Ullapool to the north-east. The 

 lower and larger portion of the quartzite, that overlies the red sand- 

 stone, is of a pure white colour on the exterior, and often vdth a polish 

 like glass, from the ice-action to which it has been exposed. In the 

 interior the rock has often a reddish tinge, from a mixture of felspar. 

 The principal constituent is however quartz, in very fine grains, rarely 

 as large as mustard seeds. Mica seems wholly wanting, or very rare. 

 Some of the beds of quartzite contain cylindrical bodies, simple or 

 branched, and from a quarter to about half an inch in diameter, 

 running vertical to the strata ; whilst others contain similar bodies, 

 but of a conical form, — both of them often in such numbers as to 

 cover the entire surface. Higher in the series a fine-grained grey 

 siliceous rock occurs, containing so much iron in layers or nodules, as 

 to become brown and rotten when exposed to the weather. The 

 surfaces of the thin layers of this rock are often marked by plant- 

 like impressions, resembling a confused mass of fucoids. I now 

 notice these markings chiefly from their importance in identifying 

 the beds, reserving their supposed organic origin to a subsequent 

 part of this paper. The quartzite is usually distinctly stratified, in 

 beds of one to two or three feet in thickness. It is also divided 

 vertically by '* backs and cutters," like those in the sandstones of 

 the coal-formation. One bed is also divided into small oblong 

 masses, like beds of clay-ironstone, but appeared to consist chiefly 

 of quartz. 



The quartzite is followed in the ascending section by a thick mass 

 of limestone, quarried in several places and cut through by the river 

 in a picturesque gorge. Even where not exposed, its presence may 

 easily be recognized by the bright green pasture that covers it. The 



* From its variable character it is difficult to give this rock a name. Probably 

 it is a felspar-porphyry or binary granite, becoming a serpentine where in contact 

 with the limestone of the quartzite. 



