and the Phenomena accompanying tlieir Elevation. 15 



few instances in which wc can obtain a view of their actual junc- 

 tion with the superincumbent beds, it is difficult to determine 

 whether they belong to a distinct formation, or must be-all re- 

 ferred to the same- 



The hill of Castro Giovanni is about two or three miles long, 

 and varies a little in breadth, has a table form, and a direction 

 sensibly parallel to that of the great chain, which runs across 

 the island to the north of it. Its eastern extremity, which is its 

 highest part J is about 2950 feet above the level of the sea *, and 

 appeared to me to be the highest point attained by the tertiary 

 rocks in this part of the country. Its upper part is composed 

 of horizontal beds of tertiary calcareous sandstone, conglome- 

 rate and coarse marl, exposing bold perpendicular cliffs all 

 round, and from the base of which there is a very rapid slope 

 to the valleys below. To the south it is separated by a deep 

 valley from another ridge having exactly the same structure, 

 but in which the beds of the summit have a very considerable 

 dip towards the south. To the north, also, we observe a simi- 

 lar arrangement ; for there the hill of Calatascibetta, which is 

 separated from that of Castro Giovanni, has the same structure, 

 and the tertiary beds which form its summit dip away in an 

 opposite direction from those on the opposite side, viz. to the 

 north. Since then, the tertiary beds on the hills both to the 

 .north and south of Castro Giovanni dip away from it as from 

 an anticlinal line ; and, since this hill is the highest point to 

 which the tertiary rocks have been elevated, I think we cannot 

 avoid the conclusion, that it was in the exact line of elevation, 

 and it ought to be kept in view, that this line is parallel to the 

 principal line of elevation in the island, viz. that of the great 

 central chain. It is also an interesting fact in connexion with 

 these views, that beds of gypsum are met with near the base of 

 the hill of Castro Giovanni on its south side, and dipping under 

 it at a very considerable angle. These different circumstances 

 will be more easily understood with the assistance of the accom- 

 panying hypothetical section (Vide PI. II. Fig. 4), where No. 1. 



• This must be taken only as a very rough approximation, for it was cal- 

 culated from two barometrical observations taken on different days, and at 

 different hours. 



