ON THE PHYSICAL GEOGRAPHY OF THE IONIAN 
ISLANDS. 
BY PROFESSOR D. T. ANSTED, M.A., E.R.S. 
•* 
Part II. 
I N a previous article I have spoken of the undrained valleys 
of Corfu, the curious salt-water midstreams of Cephalonia, 
and the remarkable weathering of detached blocks of limestone 
in several of the islands of the Ionian group, as among the 
many striking illustrations of their physical geography that 
attract the attention of the scientific traveller. These all have 
reference to the state of the limestone rock of which a large 
proportion of all the islands is composed. Limestone forms 
the ridges of the mountains, appears in innumerable broken 
fragments on the summits and sides of the hills, and may be 
found at no great depth underneath the soil of the plains. The 
islands are perfect studies of limestone, and chiefly in that form 
— half chalky, pure, but hard and very brittle — that is most 
subject to the action of water. Water dissolves it readily and 
wears it rapidly. It is full of cracks and crevices of all sizes ; 
caverns and fissures are formed in it with extreme rapidity, 
and when formed, their sides and roofs often fall in and admit 
of a more free and rapid action of the water than before. 
There is thus a perpetual change going on. 
But limestone, — that is, common carbonate of lime, — is not 
the only rock. Invarious places in all the islands, but especially 
in the north-west of Corfu (perhaps also in the southern 
extremity, which I was unable to visit), in the west of Cepha- 
lonia, and the south-east of Zante, the ordinary carbonate of 
lime is largely replaced by the sulphate, the rock consisting 
chiefly of gypsum, capable of being used for the manufacture 
of plaster, but not in fine veins of alabaster. Both in the 
neighbourhood of this rock and elsewhere there are springs 
yielding sulphuretted hydrogen gas. The condition of the 
rock, and the probability that a considerable tract of lava 
underlies the whole series of comparatively modern limestone 
in this part of the Mediterranean, render it probable that these 
gypsums and mineral springs are due to the action of vapourized 
sulphur rising from solfataras in crevices of the lava. The 
