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POPULAR SCIENCE REVIEW. 
those of the Paris Basin. The Italian geologists had also proved 
that the beds of the Super ga underlie ordinary Subapennine 
strata. Hence it became evident that the formations of the 
Falun s of south-western France, of the Super ga, and of the 
Yienna Basin, are of younger age than those of the Paris, 
London, and Hampshire Basin, and of* older date than those 
of the Subapennine hills of Italy and the Crags of England. 
It was Lyell who first recognized the remarkable significance 
which attaches to the fact that the faunas of these series of 
strata are found to contain gradually increasing numbers of 
living species as we pass upwards in the series. Brocchi had 
remarked upon the different results arrived at by Lamarck 
and himself in comparing the Paris and Subapennine shells 
respectively with those which are found living in the seas of 
the present day. But he suggested that the fact might be 
explained by the difference which undoubtedly exists between 
the testacea of the Mediterranean and those of the Atlantic 
Ocean. In 1831, when he completed the second volume of 
the Principles of Geology , Lyell had carefully considered the 
question of the gradual extinction of old forms and their re- 
placement by new ones, although, as is well known, he felt 
himself unable to accept any of the theories, which, up to that 
time, had been suggested for the explanation of the latter class 
of facts. 
All who had the good fortune to know Lyell will recognise 
it as eminently characteristic of his earnest and truth-loving 
nature that he delayed the completion of his Principles of 
Geology until he had been able to investigate personally the points 
at issue, so as to make his descriptions and reasonings as clear 
as was possible under the circumstances. In the early part of 
1828 he had already begun to feel the difficulties which beset 
the classification of the Tertiary deposits, and he spent the 
summer in examining the various districts of France and 
Northern Italy ; and in the autumn and winter of the same year 
we find him busy with the corresponding strata in the south of 
Italy and in Sicily. In 1829, on his way back to England, he 
revisited Piedmont and some of the French localities, and the 
summer of that year was devoted to the study of the English 
Crag beds. In the summer of 1830 the Tertiary deposits of 
Catalonia, the Pyrenees, and the south of France, were visited 
by Lyell ; and on his return in the autumn, six weeks were 
spent in studying the great collections of Tertiary fossils 
brought together by M. Deshay es in Paris. 
During these journeys and studies Lyell became convinced 
that the determination of the proportion of living forms in the 
marine testaceous fauna of any deposit would enable us to refer 
it approximately to its position in the geological series ; and in 
