236 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 16, 



district it is chiefly in the latter), it never breaks up the general 

 succession, which, on the contrary, is still more clearly established 

 by its persistence in spite of all such local intrusions. 



If the quartz-rocks and limestones with Lower Silurian fossils had 

 really been flanked on the east by a gneiss as ancient as that of 

 the west coast, as represented in all previous maps, they must have 

 been thrown into troughs. But nowhere, from the upper end of Loch 

 Broom in Boss-shire to the eastern shore of Loch Eriboll and the 

 northern sea-cliffs in Sutherland, is there any example that these 

 flaglike strata, whether micaceous, quartzose, or gneissose, have such 

 a reversed dip as would carry them under the Silurian quartz-rocks. 

 On the contrary, the latter are everywhere overlain by the said flag- 

 like, gneissose, or micaceous schists along a distance of seventy miles. 

 Such overlying rocks, be they ever so metamorphosed or broken in 

 upon by eruptive rock, can therefore no longer be represented on a 

 map by the same colour and with the same letter as the fundamental 

 gneiss. In fact, the term "gneiss," however good in lithological 

 parlance, must be discarded by geologists, except in a mineralogical 

 sense, just as " grauwacke " was eliminated from our nomenclature 

 when that term was found to have been indiscriminately applied 

 to rocks of various ages, from the Cambrian, through the Silurian 

 and Devonian, to the Carboniferous inclusive. In other words, the 

 day has now come, or is fast coming, when the various families of the 

 Scottish gneiss, so minutely elaborated by Macculloch, will have 

 their true ages assigned to them. 



And now a few words on strata many of them higher in the series 

 of the Northern Highlands than those already treated of. In the 

 environs of Tongue, masses of igneous rock rise out which are vastly 

 larger and loftier than any associated with the inferior portion of the 

 metamorphosed Lower Silurian rocks. Thus, it was not merely in 

 the mountains of Ben Lloghal*, to the south of Tongue, that Prof. 

 Bamsay and myself found the syenitic and granitic rocks piercing 

 through all the overlying strata having gneissose characters ; but in 

 our rapid survey we detected that the imposing mass of Ben Stomino, 

 further to the east, and which has been represented in all geological 

 maps as composed of Old Bed Sandstone, was essentially granitic ! 

 On the flanks therefore of such grand eruptive masses — and they 

 may extend over many moors and morasses where we did not follow 

 them — it was quite to be expected that the contiguous strata should 

 (as we found them) be much hardened and altered, and also often 

 twisted into devious forms, much more resembling the older gneiss 

 than any of the lower flaglike masses around Ben Hope. Yet, 

 however metamorphosed, still the order of superposition continues, 

 — the usual and prevalent dip being steadily to the E.S.E. or S.E. 

 Even in these tracts, however, the gneissose character is not per- 

 sistent ; for, on moving eastwards from the environs of Tongue to 

 the valley of Borgie Water, we again meet with interpolated mica- 

 ceous flagstones, in which undulations and ripple-marks are obser- 



* pronounced Loyal. 



