112 Geography, Geology. 



of corn, and is distinguished, even where uncultivated, by the 

 luxuriance of the plants that grow upon it. This formation, 

 though sometimes having a more arenaceous character, occurs 

 along the western coast from Trapani to Sciacca; and a 

 breccia of the same kind replete with shells, not far, if at all, 

 removed from existing species, seems to fill up the hollows in 

 most of the older rocks of Sicily. It exists at Messina, at 

 Syracuse, from whence it proceeds along the shore in the di- 

 rection of Catania, near Castro-Giovanni, and Girgenti, &c. 

 Dr. Daubeny does not decide whether the breccia found on the 

 hills in the interior of the island, is the same as that on the 

 coast between Trapani and Selinunte, but the character of the 

 rock as well as its embedded fossils appear to coincide. 



The stratum on which this reposes is by far the most con- 

 siderable in Sicily. Indeed, nearly half the surface of the 

 island is constituted of this and the subordinate beds ; as it 

 extends from the neighbourhood of Palermo and Termini on 

 the north, to Terra Nuova on the south, occupies nearly the 

 whole of the centre, and proceeds on the east to the skirts of 

 Etna. The predominating rock in this formation is a bluish 

 plastic clay, with which are associated beds of gypsum, and 

 masses of selenite, of blue limestone, of a dark brown slaty 

 marl, of a white argillaceous limestone, frequently alternating 

 with marl, and of a brecciated calcareous rock, with oval frag- 

 ments of a white compact limestone. The blue clay rarely 

 contains shells ; it possesses crystals of sulphate of lime, of 

 sulphate of strontian, and of native sulphur, rock-salt, alum, 

 sulphate of barytes, copper pyrites, and iron. 



The hill Macalubba near Girgenti is of blue clay, it is called 

 the mud or air volcano, because at times it emits a quantity of 

 gas, and throws up muddy water to a considerable height. A 

 similar chemical action takes place in the Monte di S. Calogero 

 behind Sciacca, where at its summit hot vapours * continually 

 issue from numerous crevices and clefts. At its base are hot 

 sulphureous baths, situated in the blue clay, but the mountain 

 itself is a white saccharoid limestone of a compact nature, con- 

 taining flint and shells. The blue clay formation the professor 

 believes to be of a very recent date, belonging probably to the 

 tertiary epoch, and is not related to the new red or muria- 

 tiferous sandstone of the north of Europe. 



A series of tertiary rocks occupy the southern portion of 

 the island, extending from Cape Passaro to the Lake Lentini, 

 where they are interrupted by a diluvial tract, called the plam 



* It is also singular that the same phenomena occur in the mountains of 

 Pantellaria, whiph is about seventy Italian miles distant to the south-west of 

 Sciacca. That island is, according to Ferrara, altogether volcanic. 



