242 Dr. Daubeny on the Geology of Sicily. 
Let us now consider the characters of the subjacent stra~ 
tum, which, in point of extent, is by far the most considera- 
ble in Sicily. Indeed, it might be safely said, that nearly half 
the surface of the island is constituted of this and the subordi- 
nate beds, as it extends from the neighbourhood of Palermo 
and Termini on the north, to Terra Nuovo on the south, oc- 
cupies nearly the whole of the centre, and extends 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, 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 
masses of a white compact limestone, like that which occurs 
in the Palermo rock. 
The blue clay rarely contains shells, and the only ones I 
discovered in a state sufficiently distinct to be made out, 
were a mytilus anda cardium. 1 never recollect to have seen 
it resting on any of the other beds which I have mentioned 
as being associated with it; in every instance it appeared to 
be the fundamental rock. 
The beds of gypsum found incumbent upon it rank among 
the most striking features in the geology of Sicily. They 
are composed sometimes of gypsum, sometimes of entire 
masses of selenite, which exhibit a confused crystallization. 
Plates may sometimes be detached nearly a foot in length, 
and six or eight inches in breadth.* 
The sulphate of lime occurs also dispersed ingcrystals 
through a white clay, and in cavities of the blue clay, ac- 
companied with those crystallizations of sulphate of strontian 
and of native sulphur, for which Sicily has long been cele- 
brated, 
It would appear that beds of sulphur are found every- 
where disseminated through the substance of this blue clay 
formation,f for though Sicily has long supplied all Europe 
with that mineral, its stores are as yet very far from being 
exhausted. 
* The arrow-headed variety of crystals seemed the most common. 
+ As for instance, in that of Radebaoy, near Crapina, in Croatia, 
where the sulphur is met with in balls disseminated through clay, and 
covered with marl, containing impressions of fishes, &c. the whole rest+ 
ing on the plastie clay. 
