150 THE ZOOLOGIST. 
general over the county, but, unlike its equivalent near Glasgow, 
it is a loose agglomeration of sand and hunch-backed pebbles and 
large stones. At Bloodyforeland it forms a cliff 110 feet in height, 
the matrix being a drab-coloured clay. Overlying the boulder clay 
in many places is a coarse gravel, highly charged with peroxide of 
iron; and where this is overlaid by the turf the stratum of gravel 
in contact with it is seen to be white instead of a reddish colour: 
this seems to be caused by the deoxidation of the iron by the 
organic matter in the turf. Bog-iron is to be found wherever the 
land is bleak and barren, and hundreds of tons of it are shipped 
annually to England, where it is used instead of lime for the 
purification of gas. Along the shores of Lough Swilly a light blue 
clay is found about forty feet above the present sea-level: it 
contains numerous fragments of shells, and seems to mark the old 
sea-beach. Bog is the surface deposit on a large portion of the 
county, and in some places it is as much as twenty feet deep, with 
trees occurring abundantly in it. In an island in the Rosses 
district the sea beats against a seven-feet cliff of bog, and im 
different places trees can be seen submerged, and the structures 
known as “ smelting-pots,” which were used some centuries ago for 
reducing iron, have been seen in three fathoms water. These facts 
point to a comparatively recent depression of the land, and this is 
apparently going on, although it is in no place so well marked as 
in the Rosses district. 
The influence of plant-life in modifying geological conditions is 
not so often referred to nor so well understood as its influence in 
modifying climate. An instance of the former may be noticed. 
At Glassagh, in the district of Faunett, thirteen miles from 
Ramelton, the shores at one time were very sandy, and the kelp 
made from the seaweed cast in there brought only alow price; but 
some years ago the Earl of Leitrim planted all the bare sand above 
high-water mark with bent, which has held the sand together, so 
that now enough vegetable soil has been produced as permits of 
the growth of a sward composed of Viola tricolor, Anthyllis vul- 
neraria, Erodium cicutarium, some of the coarse grasses and 
arenaceous mosses. The sand has been gradually disappearing, 
and the shore consists now of granite rock and beautiful pebbly 
strands, enabling the cottars to secure the weed free from sand, 
and to get the highest price for their produce. On the same 
Fannet coast the marine Algw may be studied without much effort, 
