CHARACTERISTICS AND DISTRIBUTION OF LAKES 577 
Peris is over three miles, but the length of the original lake must 
have been much greater, for not only is there an alluvial expanse 
stretching above the head of Llyn Peris, but a marshy flat, partly 
under water and often flooded after heavy rains, extends a good way 
below the foot of Llyn Padarn. The maximum depth recorded in 
Llyn Padarn is 94 feet, and in Llyn Peris 114 feet. The outflow of the 
lakes is bv the River Seiont to the Menai Straits. 
Bala Lake, in Merionethshire, at the head of the river Dee, is 
larger than any of those surveyed by Dr Jehu, being about Sh miles 
long by three quarters of a mile broad; and one still larger. Lake 
Vyrnwyn, an old lake artificially enlarged in order to increase the water- 
supply of Liverpool, was constructed about twenty years ago by 
building a dam, 1165 feet long, to hold back the head- waters of the 
Vyrnwyn River, a tributary of the Severn. This lake is capable of 
holding 2103 million cubic feet of water. 
Many lakes of considerable extent exist both in the mountainous Ireland, 
and lowland districts of Ireland, and the number of small lakes is 
very great. The total area covered by lakes amounts to 711 square 
miles. Careful surveys have been made by the Admiralty and maps 
published between the years 1835 and 1854 of the principal lakes, 
viz. Loughs Neagh, Mask, Corrib, Derg, Ree, and Erne (Upper and 
Lower), and also of the smaller Lough Derg in County Donegal. 
Lough Neagh, in the province of Ulster, the largest lake in the 
British Isles, receives the Upper Bann, the Blackwater, and numerous 
other streams, and discharges by the Lower Bann into the North 
Channel at Coleraine. It is 17 miles in length, about 10 miles in 
breadth, and covers an area of 153 square miles ; it lies 48 feet above 
sea-level, and has a mean depth of 40 feet and a maximum depth of 
102 feet. The islands are few and small, and the shores, particularly 
on the south, are flat and mai-shy. It lies in a volcanic area in a 
basin formed by fracture and subsidence. It is well stocked with 
fish — like trout, char, pullen.^ Canals extend from Lough Neagh to 
Belfast, Newry, Tyrone, and Lough Erne. 
Lough Mask, on the borders of Mayo and Galway, receives the 
waters of the River Robe, and the surplus waters of Lough Carra to 
the north-east of it and of Lough Nafooey to the west* and is drained 
by an underground stream into Lough Corrib. It is 35 square miles 
in area, 10 miles in length by 4 miles in breadth, with a maximum 
depth of 191 feet. Its elevation above sea-level is about 50 feet. 
Lough Corrib, lying at an altitude of only 14 feet above sea-level, 
nearly divides County Galway into two parts. It is very irregular in 
shape, and contains many islets. It has a maximum depth of 152 
^ For analysis of the water of Lougli Neagh, see p. 149. 
37 
