584 GEOTECTONIC (STRUCTURAL) GEOLOGY. [Boox IV: 
stone (c) dipping below a series of quartz-schists and micaceous flag- — 
stones or flagey mica-schists (d). This order of succession is visible in 
many magnificent natural sections for a distance of ninety miles. The 
Lower Silurian age of these rocks is fixed by the occurrence of recog- 
nizable fossils in the lower parts of the series. The basement quartzite is 
full of annelide-lurrows ; the limestone has yielded Maclurea, Murchisonia, 
Ophileta, Pleurotomaria, Orthis, Orthoceras, and Piloceras ; the shales are 
crowded with carbonaceous fucoid-like casts. On the whole, these 
fossiliferous strata are not much altered, but as the fissile series overlying 
them is traced eastwards, it is found to assume a more schistose character. 
The original stratification remains indeed quite distinct; bands of more 
sandy nature alternating with others of a more argillaceous composition, 
as sandstones and shales do elsewhere. Some of the strata are made up 
of water-worn pebbles of quartz, &c., in a schistose matrix. Even the 
false bedding of the sandy beds can readily be detected. With these 
evidences of an original clastic character, there is noticeable a fine 
foliation produced by the development chiefly of minute folia of mica 
in the planes of deposit. So long as the strata retain their gentle 
easterly inclination this foliation remains feeble and with little variation. 
But after passing across several thousand feet of these little -altered 
strata, we find that they rapidly undergo a series of plications, after 

Fic. 300.— DIAGRAM OF THE ORDER OF SUCCESSION AMONG THE CRYSTALLINE-SCHISTS 
OF SCOTLAND, 
which their angle of inclination remains high for a long distance, 
are thrown into numerous steep arches and troughs (e). 
With this change from a gentle and scarcely disturbed succession to a 
highly plicated and crumpled condition, there is an accompanying and 
proportionately rapid increase in crystalline character. The rocks become 
thoroughly foliated mica-schists and fine gneisses, containing porphyritic 
crystals of orthoclase and garnet with concretions and veins of quartz. The 
rest of the Highlands to the east and south is overspread by a continua- 
tion of these same rocks. By numerous anticlinal and synclinal foldings 
quartzites and limestones are brought to the surface, but are almost always 
more crystalline than the rocks of the north-west. The cr ystalline condi- 
tion, however, is by no means uniform. In certain regions argillaceous 
beds occur which are rather shales than schists, so little have they been 
changed. These beds elsewhere pass into spotted schists and andulusite- 
schists. ‘The limestones often occur, as they do in Sutherlandshire. in 
association with white quartzites ; sometimes they are grey, granular and 
finely crystalline, sometimes they appear as white marble containing 
garnet, idocrase, tremolite, zoisite, and many other silicates. The altera- 
tion has thus been remarkably unequal over the whole region, and has 
reached the maximum development sporadically, particularly where the 
strata exhibit proofs of intense crumpling. It is deserving of remark 
that the rocks along the southern margin of the Highlands are for the 
most part comparatively little altered, and that they dip towards the 
as they 
