590 HISTORY OF GEOLOGY. 



was in some measure obscured. But it was not long before a very 

 able attempt was made to obliterate it altogether. In 1828, Mr. Lyel 1 

 set out on a geological tour through France and Italy.' He had 

 already conceived the idea of classing the tertiary groups by reference 

 to the number of recent species which were found in a fossil state. 

 But as he passed from the north to the south of Italy, he found, by 

 communication with the best fossil condhologists, Borelli at Turin, 

 Guidotti at Parma, Costa at Naples, that the number of extinct species 

 decreased ; so that the last-mentioned naturalist, from an examination 

 of the fossil shells of Otranto and Calabria, and of the neighboring 

 seas, was of opinion that few of the tertiary shells were of extinct spe- 

 cies. To complete the series of proof, Mr. Lyell himself explored the 

 strata of Ischia, and found, 2000 feet above the level of the sea, shells, 

 which were all pronounced to be of species now inhabiting the Medi- 

 terranean ; and soon after, he made collections of a similar description 

 on the fiauks of Etna, in the Val di Noto, and in other places. 



The impression produced by these researches is described by him- 

 self. 7 " In the course of my tour I had been frequently led to reflect 

 on the precept of Descartes, that a philosopher should once in his life 

 doubt everything he had been taught ; but I still retained so much 

 faith in my early geological creed as to feel the most lively surprize on 

 visiting Sortiuo, Pentalica, Syracuse, and other parts of the Val di 

 Noto, at beholding a limestone of enormous thickness, filled Avith 

 recent shells, or sometimes with mere casts of shells, resting on marl 

 in which shells of Mediterranean species were imbedded in a high state 

 of preservation. All idea of [necessarily] attaching a high antiquity 

 to a regularly-stratified limestone, in which the casts and impressions 

 of shells alone were visible, vanished at once from my mind. At the 

 same time, I was struck with the identity of the associated igneous' 

 rocks of the Val di Noto with well-known varieties of ' trap ' in Scot- 

 land and other parts of Europe ; varieties which I had also seen enter- 

 ing largely into the structure of Etna. 



" I occasionally amused myself," Mr. Lyell adds, " 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." 



9 1st ed. voL iii. Pref. T Lyell, 1st ed. Pref. x 



