34 TRANSACTIONS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
length of the constituents of a river system as the most important 
factor, and the system should be viewed as a whole series of con¬ 
verging channels. 
GEOGRAPHICAL. 
In a corrie on the side of Ben I.ui, nearly midway between 
Tyndrum and Dalmally, at a point almost exactly 3000 feet above 
sea-level, the River Tay takes its rise. Impetuosity is the charac¬ 
teristic of its infancy, because before it has travelled a distance 
of II miles, it has descended to an elevation of only 500 feet. Down 
to this point it has been known as the Fillan Water, and here enters 
Loch Dochart, a sheet of water about three miles in length. After 
flowing from this loch for another course of 11 miles, during which 
its name is changed to the Dochart, it enters Loch Tay below Killin. 
From the eastern end of Loch Tay 14^ miles distant, the river, 
issuing from the loch at Kenmore, for the first time assumes the 
title of the Tay. For the remainder of its existence the Tay pursues 
a sober and- dignified course, gradually augmenting in volume and 
power, quietly absorbing stream after stream, and sweeping silently 
along, except when forcibly restrained, as in the case of the barrier 
of volcanic rock which impedes its progress at Campsie Linn. At 
length its expanded waters merge into the North Sea eight miles 
below Dundee, after a total journey of 117 miles from its most 
distant source. The chief distances may thus be summarised :— 
Source to Loch Tay, 
Head of Loch to Kenmore, - 
Kenmore to junction with Garry, - 
Junction with Garry to Perth Bridge, 
Perth to mouth, - - - - 
25 miles. 
14J „ 
isi .. 
117 miles. 
After leaving Loch Dochart the gradient of the river, or its fall in 
elevation, becomes comparatively slight. The surface of Loch Tay 
is 350 feet above sea level; at the junction with the Garry, the height 
is 200 feet; and at a point about a mile above Perth, elevation may 
be said to disappear, for the Tay has become a tidal river. Twice in 
its course the Tay changes its direction in a very marked manner, 
giving rise to three distinct divisions. Starting from the source, its 
direction is north-easterly until it is joined by the Garry. There it 
turns almost at right angles, and assumes a direction mainly south¬ 
easterly across the vale of Strathmore until it reaches Perth. It 
there takes another sharp bend and flows nearly east until it reaches 
the sea. Attentive study of a map may show the causes which 
