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and are consequently spread over wide areas. Now wliile the 
methods of William Smith proved so successful when applied 
to the uniform and widely-spread deposits of older date, it was 
soon found exceedingly difficult, if not impossible, to trace the 
order of superposition, and to represent on maps the outcrops 
of the inconstant patches of sand, clay, and shell-hanks, which 
often make up the Tertiary formations. 
It is to the late Sir Charles Lyell that geologists are 
indebted for the suggestion of a method whereby the local 
and inconstant patches of Tertiary strata, which are scattered 
all over Europe, might be brought into comparison with one 
another and arranged in groups according to their relative 
ages. The discovery of this method of classifying the Tertiary 
strata was an achievement only second in importance to William 
Smith’s determination of the order of succession among the 
Secondary formations, and would, of itself, serve to place Ly ell’s 
name in the foremost rank among the founders of the science 
of Geology ; even apart from the claim which he derives from 
his masterly exposition of the philosophy of the science con- 
tained in the immortal Principles of Geology. 
The study of the Tertiary formations, as of so many other 
branches of Geology, was commenced in Italy. After the great 
discussions as to the true nature of fossils, which occupied the 
minds of the thinkers of that country during the seventeenth 
century, had been brought to an end by the general acceptance 
of the doctrine that fossils are not accidental simulacra, but actual 
relics of once living beings, many able naturalists turned their 
attention to the study of the rich series of fossils contained in 
the Subapennine strata. Soldani, Testa, Fortis, Cortesi, Spal- 
lanzani, and other Italian naturalists, all recognized the im- 
portant fact, that while some of the fossils found in the Sub- 
apennine strata are referable to forms still living in the 
Mediterranean, others are now only found in tropical seas, 
while others again have never been discovered among recent 
forms and are presumably extinct. 
At the commencement of the present century, the illustrious 
Italian geologist, Brocchi, had made a very extensive collection 
of the Subapennine fossils, and by a comparison of these with 
recent shells, he had arrived at the conclusion that more than 
one half of the Subapennine forms are still living in the 
Mediterranean, or in other seas, chiefly those of hotter climates. 
The labours of Brocchi were supplemented by those of Bonelli, 
Guidotti, and Costa, who added greatly to our knowledge of 
the several Subapennine faunas. 
While this important work was being carried on in Italy, 
naturalists were not idle in other parts of Europe. Cuvier and 
Brongniart described the succession of strata in the Paris Basin, 
