PREFACE. 
limestone, in which the casts and impressions of shells 
alone were discernible, vanished at once from my 
mind. At the same time, I was struck with the iden- 
tity of the associated igneous rocks of the Val di Noto 
with well known varieties of ' trap ' in Scotland and 
other parts of Europe, varieties, which I had also 
seen entering largely into the structure of Etna. I 
occasionally amused myself with speculating on the 
different rate of progress which Geology might have 
made, had it been first cultivated with success at 
Catania, where the phenomena above alluded to, and 
the great elevation of the modern tertiary beds in 
the Val di Noto, and the changes produced in the 
historical era by the Calabrian earthquakes, would 
have been familiarly known. 
From Cape Passaro I passed on by Spaccaforno and 
Licata to Girgenti, where I abandoned my design of ex- 
ploring the western part of Sicily, that I might return 
again to the Val di Noto and the neighbourhood of 
Etna, and verify the discoveries which I had made. 
With this view I travelled by Caltanisetta, Piazza, 
Caltagirone, Vizzini, Militello, Palagonia, Lago Naftia, 
and Radusa, to Castrogiovanni, and from thence to 
Palermo, at which last place I procured the shells 
named in Appendix II. p. 55. The sections on this 
new route confirmed me in my first opinions respecting 
the Val di Noto, as will appear by the 6th, 8th, and 
9th chapters of the third Volume. 
When I again reached Naples, in January, 1829, I 
