207 
ON THE BOTANY OF I,OUGH CARRA. 
BY K. U.OYD PRAKGKR. 
lyOUGii Carka is one of the chain of lakes which runs fi-om 
Gahvay Bay to Killala Bay, intervening between the great 
limestone plain, which stretches away to the eastward, and 
tlie Connaiight highlands, formed largely of metamorphic and 
igneous rocks, which rise, often abruptl}^ on the western side 
of the lake-basins. While not attaining anything like the 
size of Corrib, Mask, or Conn, I^ough Carra is nevertheless a 
good-sized sheet of water. It has a length of six miles and a 
breadth of two, but is much broken up by promontories and 
islands. One large land projection almost cuts the lake in 
two, and as there are certain differences of character between 
the two portions, I shall distinguish them as the upper (/.^., 
northern) lake and lower (z.^., southern) lake respectively. Lough 
Carra lies just inside the western boundary of the limestone 
area, which runs north and south within a mile of the lake- 
shore. The strip of Carboniferous Sandstone, a couple of 
miles wide, which then intervenes between the limestone of 
the plain and the slates, gneisses, and porphyries of the 
mountains, supports the full calcifuge flora which charac- 
terises the latter. Around the lake the limestone dips east 
and south-east at very low angles — generally about 3° — which 
tends to produce shallow water on the eastern side of the 
islands and pointvS, while the western side often descends 
steeply into deeper water. The lower lake is mostly very 
shallow, the upper lake deeper, and with higher shores, 
lyough Carra has long been famous for the wonderful colour 
of its water, which is a pale pellucid green. This results 
partly from the purity of the water itself, but mainly from the 
extraordinary limy incrustation which covers the whole 
bottom. Even on the boulders just below water-level this is 
an inch or two in thickness — a soft crust, with pinkish and 
greyish blotches caused by algal growth. Deeper down the 
deposit is softer and more soapy in feel, and white or cream 
in colour. The incrustation is most dense in the lower lake, 
and has there a very deleterious effect on aquatic plant-life. 
Hydrophytes are nearly absent, and a few starved beds of 
