THE FRESH-WATEK LOCHS OF SCOTLAND. 205 



THE LOCHS OF LEWIS. 



THE island of Lewis and Harris is the largest of the lesser British 

 islands (see Index Map, Fig. 23), only Skye and the Mainland of Shetland 

 nearly approaching it in size. It measures some 60 miles in length by 

 30 miles in breadth. Its southern half is mountainous, many peaks 

 exceeding 2000 feet in height, and a few exceeding 2500 feet. The 

 northern half is lower. 



There are many hundreds of lochs distributed over every part of the 

 island. In the northern half they are specially numerous, and in the 

 central part they form a sort of watery maze like that of North Uist. 

 There are only a few of the narrow, straight, valley lochs, so familiar 

 on the mainland of Scotland, and those are in the southern mountainous 

 part of the island ; the majority are small, roundish, or relatively broad, 

 and the larger ones of extremely irregular form. It was only possible 

 to survey a small proportion of the numerous lochs, thirty altogether 

 being sounded. 



Five of the lochs exceed 2 miles in length. Loch Langavat is by far 

 the longest, exceeding 7 miles, and in superficial area is about four times 

 as great as any other loch. It is, however, exceeded in volume by Loch 

 Stiainaval, which contains 2843 millions of cubic feet. Loch Suainaval 

 is also by far the deepest loch, exceeding 200 feet in maximum depth, 

 while no other loch exceeds 100 feet. Five lochs, Langavat, Scaslavat, 

 Grunavat, Benisval, and Raonasgail, approach 100 feet in depth. The 

 mean depth of Loch Suainaval is 108 feet, no other loch exceeding 35 

 feet. Combining the areas of all the lochs, the extent of fresh water sur- 

 veyed amounts to nearly 10 square miles, the volume of water to 7400 

 millions of cubic feet. 



The thirty lochs of Lewis surveyed are contained in seventeen distinct 

 basins, draining independently into the sea. Twelve of these basins 

 contain only one loch which was surveyed ; three contain two lochs ; the 

 Thamanabhaidh basin contains four lochs ; the most extensive basin sur- 

 veyed is the Laxey basin, with its eight lochs. Many extensive basins 

 were not visited at all. 



There follows a table of the seventeen basins and the lochs contained 

 in them : 



