THE FRESH-WATER LOCHS OF SCOTLAND. 
267 
Castle Semple Loch (see Plate CXXXIII.) is a fairly large loch, in the 
county of Renfrew, about 15 miles west of the city of Glasgow. The 
north shore is wooded, and there is a sparse strip of trees on the south 
shore also, between the loch and the railway. The loch is of narrowly 
triangular form, broadest near the west end, and measures If miles in 
length, and a little more than one-third of a mile in breadth. It is 
extremely shallow and flat-bottomed, 6 feet in maximum depth, and 
feet in mean de]3th. The area is about 203 acres, or one-third of 
a square mile, and the volume 22 millions of cubic feet. Castle Semple 
Loch receives the drainage of an extensive area (nearly 36 square milesj, 
chiefly brought from the hills to the west by the river Calder, which 
enters the west end of the loch. The Black Cart water issues from 
the east end of the loch, and, after flowing 10 miles to the north-east, 
enters the Clyde 3 miles north of Paisley. 
The level of the surface on May 7, 1896, was found by the Ordnance 
Survey to be 89-6 feet above the sea. The temperature was 60°*0 Fahr. 
throughout on July 21, 1906. 
Upper Gryfe Beservoir (see Plate CXXXIV.). — The Gryfo reservoir, 
which lies 3 miles south of Greenock, and immediately to the east of Loch 
Thom, has been formed by draining the upper portion of the valley of the 
Gryfe, and is a part of the Greenock Waterworks. The surroundings are 
moorland and pasture. The north shore rises more steeply from the loch. 
When full the length is Ij miles, but on the date of the survey (October 8, 
1906) the loch was very low, and was only about a mile long. The greatest 
breadth at the east end was fully one-third of a mile. The maximum 
depth close to the dam was 34 feet, and the mean depth over 17 feet. The 
superficial area was about 115 acres, and the volume 87 millions of cubic 
feet. The drainage area is 2h square miles. The river Gryfe flows east- 
ward about 12 miles, and joins the Black Cart near Paisley. The 
elevation was 598*2 feet above sea-level. 
Loch Thom (see Plate CXXXIV.) is a large artificial loch, the principal 
reservoir of the Greenock Waterworks, lying at an elevation of 632 4 feet 
above the sea among the hills some 3 miles south of Greenock. It is 
surrounded by moorland, and there are one or two farms on the shores. 
The loch was very low at the time of the survey (Augnst 16, 1906), and 
the large island near the east dam was joined to the shore. The length, 
measured in a straight line from north to south, is 1^ miles. The axis 
of the loch is strongly curved. The greatest breadth, about the middle of 
the loch, is half a mile. The depth is greatest in the northern part, and 
the maximum depth of 42 feet is near the northern end of the loch. The 
mean depth is 191 feet, the area about 331 acres, or half a square mile, and 
the volume 277 millions of cubic feet. The drainage area is about 5^ 
square miles. 
The temperature was identical (60°' 0 Fahr.) at the surface and at 35 feet. 
