1858.] MTJECHISON NORTHEEN HIGBXANDS, ETC. 371 



eroded edges of the latter is seen to repose the lower quartz-rock (c^) 

 in thin flat-bedded strata usually weathering white, but here and 

 there of a pinkish colour. It was in the higher part of this band 

 that Professor Sedgwick and myself (1827), and Macculloch before 

 us, observed certain cylindrical bodies, now known (as before ob- 

 served) to be due to Annelides. Dipping to the E.S.E., these rocks 

 are carried under the great mass of the limestone of Durness (c^), 

 which occupies several ridges over a maximum width of about three 

 miles. 



Examining its ridges both longitudinally and transversely, Mr. 

 Peach pointed out to me, and particularly in the hard, cherty, and 

 cavernous portions of the rock, mstnj Maclurece and a* great abun- 

 dance of Murchisonice, with some Orthocerata. These fossils inva- 

 riably occur in dark-coloured cherty and very fetid limestone, which 

 occasionally presents a rugged outline as it peers through the rich 

 grass of tMs sheep-feeding-ground. Some of the exposed points or 

 knobs, which weather black, are surrounded or partially wrapped 

 over by a tufa-like siliceous sinter, sometimes resembling a breccia, 

 which conveys the idea of a boiling over of such matters when the 

 rock underwent the metamorphism to which it has evidently been 

 subjected. Even in this peculiarly hard matrix, my companion 

 detected traces of fossils. The most marked of the external cha- 

 racters of the limestone is its coarse rugosity — the result probably 

 of weathering upon its peculiar composition, and which gives the 

 scarps of the rock the appearance of an elaborately wrought rustic 

 basement of a Plorentine palace. The best limestone is in the state 

 of a cream-coloured compact marble ; but no fossils have been dis- 

 covered in that variety of the rock. Even in its siliceous condition, 

 the Hmestone occasionally retains an oolitic structure. 



Owing to breaks, undulations, and twists, it is difficult to form even 

 a tolerably accurate estimate of the united thickness of all these beds 

 of hmestone ; but in Durness, where they occupy successive terraces 

 with little intervening grassy valleys, they cannot well be less than 

 500 or 600 feet thick. If the section be extended to the Old Bishop's 

 Castle on the east (fig. 6), the observer finds that, after passing over 



Fig. 6. — Section of the Upper Quartz-rock to the east of Durness, 



W. Old Bishop's Castle. E, 



c2. Durness fossiliferous linaestone, 

 c^. Quartzose and micaceous flagstones. 



a low ground covered by blown sand (the usual position of the 

 upper quartz-rock in other places), he reaches a headland composed 

 of overlying thin-bedded grey micaceous flagstone (c^), which occa- 

 sionally weathers white, like the promontory of the Whiten Head on 

 the opposite side of the bay. 



