460 THE FRESH-WATER LOCHS OF SCOTLAND 
extending from Glenelg to Strath Conan and along the Great Glen 
are striking examples of the latter. 
On the eastern portion of the Northern Block the grain of the 
younger strata tended to deflect the rivers from their south-east 
course. The disposition of the Old Red Sandstone and the mesozoic 
strata not only shows that they must have entered largely into the 
structure of the High Plateau, but also that they were thrown into 
two basins intersected by the Great Glen fault, the axes of these 
basins being approximately north-east and south-west. In these 
weak structures the grain of the rocks became a prominent factor in 
deflecting the rivers from theu' south-east course, and, during the 
period of maximum elevation, in reducing the area to a plain in 
which the old divides were nearly obliterated. From a studv of 
charts of the sea floor it would appear that two main trunk rivers 
were established, following the strike of the weak strata and the 
shatter belts produced by the Great Glen fault and the dislocation 
skirting part of the Sutherland coast. The more northerly one seems 
to have flowed parallel to the present coast-line of Sutherland, 
Caithness, and Oi'kney, intercepting all the consequent streams as far 
south as the Dornoch Firth and ultimately draining into the Faroe 
Channel ; the other parallel to the coast of Nairn, Moray, Banfl', and 
Aberdeen, following what is probably the strike of the secondary 
strata, and at one time, either directly or by means of longitudinal 
tributaries, tapping all the consequent rivers westwards to Loch Eil. 
The Cromarty Firth is evidently the submerged valley of a 
subsequent stream following the centre of the svncline between the 
two great shatter belts, which intercepted and deflected all the old 
consequent streams now draining into it. Again, the main subsequent 
river between Inverness and Nairn, whose course is now covered by the 
Moray Firth, tapped and deflected the consequent stream which 
formerly occupied the site of the Beauly Firth. 
Along the eastern portion of the Northern Block the intermediate 
plateau and the coastal belt are mainlv carved out of Old Red 
Sandstone, but in certain localities thev consist of the old floor of 
crystalline schists from which the covering of Old Red Sandstone has 
been removed. Various outlying masses of this formation furnish 
striking proof of its former extension over the high plateau of the 
Northern Block, as for instance in Strath Vaich, Ross-shire, the 
heights on either side of Strath Brora, and the Griams in Sutherland. 
The development of the plain of North Sutherland and Caithness 
resembles in many respects that of East Sutherland and Easter Ross. 
Here the weak strata that remain are composed of Old Red Sandstone. 
A main trunk stream appears to have cut back from the Faroe 
Channel, west of and parallel to the long axes of Shetland and 
