GREAT GLEN OF SCOTLAND. 
203 
unbroken outline throughout its whole extent, of about 
twenty miles. 
The height of this ridge is from 300 to 500 feet, and 
the acclivities on both sides are gentle, and covered with a 
deep bed of alluvium. The cover of alluvial matter is so 
considerable, as in general to conceal the strata, thus leav- 
ing us as the only means of becoming acquainted with them, 
the inspection of quarries. Judging from these quarries, 
the whole range appears to be distinctly disposed in strata, 
generally slightly inclined to the horizon, and composed of 
slate-clay inclining to clay-slate, red sandstone, and occa- 
sionally conglomerate, sometimes bearing a considerable 
resemblance to grey wacke ; and, like some of the varieties 
of sandstone, bearing marks of being in part the results of 
a process of crystallisation. 
In these strata, a few simple minerals are met with, such 
as arragonite, heavy spar, calcareous spar, and iron- 
pyrites. 
Alluvia. 
The mountainous ranges encircling Inverness, I have 
shewn to consist of gneiss, granite, syenite, quartz-rock, 
slate-clay, red sandstone, and conglomerate ; and it now 
seems necessary, for their final elucidation, to describe the 
characters of the alluvial matters in the Great Valley sur- 
rounded by these mountains. 
The principal part of this space is covered by the waters 
of the Moray Frith and Loch Ness, and the remainder 
forms the bed of the Caledonian Canal. 
At Fort Augustus, the highest point of this extensive 
Valley, an alluvial collection, composed of the debris of the 
neighbouring mountains, spreads itself between the Lakes 
