THE FBESH-WATER LOCHS OF SCOTLAND. 267 



Castle Semple Locli (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, 5 feet in maximum depth, and 

 2J feet in mean depth. 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 miles), 

 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 6u'0 Fahr. 

 throughout on July 21, 1906. 



Upper Gryfe Reservoir (see Plate CXXXIV.). The Gryfe reservoir, 

 which lies 3 miles south of Greenock, and immediately to the east of Loch 

 Thorn, 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 1| 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 2J 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. 



LocJi Thorn (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 1J 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 19J feet, the area about 331 acres, or half a square mile, and 

 the volume 277 millions of cubic feet. The drainage area is about oj 

 square miles. 



The temperature was identical (60'0 Fahr.) at the surface and at 35 feet. 



