Chap. XI.] OLD RED SANDSTONE OF N.-E. OF SCOTLAND. 
253 
the older system be viewed in the western part of Sutherland and Eoss, 
where limestones are intercalated in quartzites, or in the eastern tracts of 
those counties, where gneissose and micaceous schists prevail, the strike 
which is most frequent is seen to be from N.N.E. to S.S. W., the dominant 
dip being to the E.S.E. The Old Red conglomerate of the east coast is, 
on the contrary, thrown off the promontories of the older system in devious 
directions, the prevailing dip in Caithness being to the N. of E. (and even 
N.N.E. ), in the northern part of Ross-shire to the S.S.E., and on the south 
side of the Murray Erith again to the N.N.E. A complete unconformity, 
in short, is everywhere observable, independent of the fact that the 
younger deposit is literally made up of the debris of whatever portion of 
the older it happens to rest upon. In this way we observe that in one 
spot the conglomerate is chiefly made up of quartz-rock ; in another, of 
mica-schist ; in a third, of gneiss ; in a fourth, of granite ; and occasionally 
of all these and other varieties of the older system mixed together. 
Then, again, nothing can be more dissimilar than the physical outlines 
of these two rock-systems. "Whilst the quartzo-micaceous, crystalline 
rocks resemble in outward form a tumultuous sea, the observer who stands 
on the conglomerate which lies on their eastern edges sees beneath him, 
to the east, the highly contrasting outline of soft undulations which, in 
the low countries of Caithness, Easter Ross, Inverness, Nairn, and Elgin, 
dip gradually away to the seaboard. So strong is this contrast, that the 
geographer unacquainted with geological science would at once say that 
these two rock-systems belonged to very different epochs in the history of 
the earth's crust. 
In no tract of Britain, indeed, is there so clear a succession of the 
whole group of the Old Red Sandstone, properly so called, as that which 
is exposed on the north-eastern shores of Scotland. This order is espe- 
cially well seen when the observer, having made himself well acquainted 
with the copious lower conglomerates and sandstones which fringe the 
crystalline rocks of Elgin, Nairn, Inverness, and Ross-shire, passes 
through Sutherland into Caithness and the Orkney Islands. This last is 
the region selected thirty years ago by Professor Sedgwick and myself * 
as affording what we then conceived to be the clearest example of the 
extended features of that great group of the British series with which we 
long afterwards compared, as an equivalent in time, the slaty rocks, schists, 
sandstones, and limestones of Devonshire. (See pp. 271 &c.) Having 
twice revisited the north-east coast of Scotland since the first edition of 
this work was published, and having been confirmed in my former views 
concerning the general physical succession of the masses, a brief sketch of 
the leading phenomena is now given. This resume is the more called for, as 
geologists who have never examined this north-eastern region, and have been 
* Trans. G-eol. Soc. Lond., 2nd ser., vol. iii. p. 125, with map of the Highlands, sections, and some 
figures of the Caithness Fishes. 
