14 ON CHANGES IN THE DISPOSITION 



who prefer illustrations of higher and foreign name 

 may read of; commonly with little useful under- 

 standing of the subjects, and, too often giving their 

 faith to doubtful recorders and to makers of hypo- 

 theses. Any map of the great rivers of the world will 

 show the extent and places of that system of connected 

 and successive levels which conducts water from its 

 several sources to the sea. There are such systems, 

 whose perfection is owing to the action of the rivers 

 which they now conduct in so smooth a manner: 

 there are others which, interrupted by lakes and 

 cataracts, indicate what nature did at first, and w r hat 

 the river has yet to do. These last are the instructive 

 ones ; and, in our own island, the Tay is an epitome 

 of every thing : but he who desires to understand, 

 must examine what I can but indicate in a small por- 

 tion of its multifarious branches. The Dochart is 

 fast filling its lake, and will in no long time hold its 

 uninterrupted course through that valley : long yet 

 however to fall into Loch Tay, through that suc- 

 cession of cataracts at Killin, which, did they retreat 

 faster than the lake fills, woiild produce an example 

 of the drainage of lakes. Contrasted with this, the 

 Lochy has finished the working out of its bed, and 

 now enters the lake, at the same place, a sluggish 

 stream. That lake is the first great interruption in 

 the Tay; and centuries must yet pass before it will 

 here have formed its own bed. In the small streams 

 that join the Lyon, we find every mode of the vertical 

 torrent and fissure ; and the ravine of the Keltnie de- 

 monstrates the depth to which water can act on the 

 solid rocks. The cascades of Moness show what the 

 original courses of all mountain waters must have 

 been, as the great cataract of the Turn el will explain 

 the proceedings of Niagara: while they who will 

 pursue this branch to its source in Rannoch, will see 



