384 PEOCEEBINGS OF THE GEOLOaiCAL SOCIETY. [DeC. 1, 



to the E.S.E., and contain garnets, whilst the lower part of the very 

 same mountain is a true quartz-rock. 



To the east of Tongue there is indeed a great sameness of such 

 crystalline strata, which are inclined at low angles of not more 

 than 10° or 12° ; but at Naver the micaceous quartzose flags with 

 garnets dip 60°, and at Farr as much as 70°. Thenceforward, in 

 travelling eastward, intruding bosses of a granite similar to that 

 noticed by Mcol and myself at the head of Loch Eribol again 

 prevail ; and some of these (as formerly described by Sedgwick and 

 myself) not only penetrate the crystalline strata, but also throw off 

 the overlapping Old Eed Sandstone and Caithness Flags. 



In Caithness the explorer enters into a region of essentially dif- 

 ferent structure, and consequently of an entirely different outline. In 

 the very first quarries of the overlying sandstones and flagstones 

 which he reaches, the traveller finds no longer a S.E. or E.S.E. 

 dip, but one to the N. or N.W., or athwart the older rocky series on 

 wliich he has been wandering. When the quartzo-gneissose series 

 is followed southwards, by Ben na Ghream along the western flank 

 of the flat and monotonous county of Caithness, we come to that 

 remarkable group of mountains called the Scarabins, which are ob- 

 viously a portion of the upper member of the same crystalline series. 

 Here crystalline quartz-rock prevails, weathering pure white, and 

 of a different character from the quartz-rocks of the west, being 

 probably the result of the intrusion of the great masses of granite 

 which there abound. 



The manner in which the base of the Old Eed Sandstone overlaps 

 these quartz-rocks was long ago described by Sedgwick and myself*. 



AU around the Scarabins, and particularly to the east of Berridale, 

 the most striking discordance is seen in the relative strike and dip of 

 these two groups, — the quartz-rock, or associated gneissose strata, 

 being inclined sharply to the W.S.W., or to the south by east, whilst 

 the Old Eed conglomerate and sandstone dip away east and north, 

 and also to the west, at 10° and 12° only. 



In hke manner, when we proceed on the true dip of the older rocks 

 from Loch Assynt on the W.IS'.W., and follow the coiu'se of the 

 Oikel Eiver from Sutherland into Eoss, we meet with a great rupture 

 and a complete unconformity of stratification at the junction with 

 the Old Eed Sandstone. Hence, setting aside partial disturbances 

 at various horizons, as resulting from the eruption of igneous rocks, 

 we see that all the crystalline and subcrystaUine strata from the 

 west up to this great and general break, and which are intercalated 

 between the Cambrian Conglomerates beneath and the true Old Eed 

 Sandstone above, must belong to one and the same great natural 

 division ; for they are, on the whole, conformable to each other in 

 their strike, undulations, and inclination. Even if no fossils had been 

 found in them, it was probable that, being placed between a con- 

 glomerate of very high antiquity, on the lower or western side, and 

 the base of the Old Eed Sandstone on the other, these quartzose 



* See Trans. Greol. Soc. 2nd ser. vol. iii. p. 128. 



