286 Sutherland and Caithness. 



to those that have been mentioned respecting the un- 

 conformity of the Cambrian on the Laurentian rocks. 

 In both a great interval of time is indicated un- 

 represented by stratified formations. The bottom 

 beds of the Lower Silurian strata consist of quartz- 

 rock and two beds of limestone (3), the latter so 

 altered that the fossils are sometimes with difficulty 

 distinguishable, even by those most skilled in the 

 determination of genera and species. Above the 

 upper limestone we have a vast series of beds of mica- 

 schist and gneissose rocks (4), mostly flaggy in the 

 north-western region, but, in the eastern parts of Suther- 

 land and Aberdeenshire, often so highly contorted and 

 metamorphosed that they are, in some respects, similar 

 to the more ancient Laurentian gneiss. 



Now these metamorphosed Silurian rocks, here and 

 there associated with bosses of granite and syenite (g\ 

 form by far the greater part of that rocky region known 

 as the Highlands of Scotland, which stretches over 

 brown heaths and barren mountain ranges, all the way 

 from Loch Eribol on the north shore, far south across 

 the Grampians, to the Firth of Clyde on the west, and 

 Stonehaven on the east. 



In Sutherland, as a whole, the Silurian strata dip 

 eastward, and in Caithness we have the Old Eed Sand- 

 stone (5) lying quite unconformably upon the Silurian 

 gneiss, and dipping towards the sea. At its base the 

 Old Red Sandstone consists of conglomerate, not 

 formed merely of small pebbles, like those of an ordinary 

 shingle-beach, but frequently of huge masses, suggestive 

 of ice-borne boulder-beds, mingled with others of 

 smaller size. All of them have evidently been derived 

 from the partial destruction of those ancient Silurian 



