XlV PREFACE. 
arranged in a chronological series. I accordingly lost 
no time in seeing M. Deshayes, who explained to me 
the data on which he considered that the three ter- 
tiary periods mentioned in the Tables, Appendix I., 
might be established. I at once perceived that the 
fossils obtained by me in my tour would form but an 
inconsiderable contribution to so great a body of 
zoological evidence as M. Deshayes had already in 
his possession. I therefore requested him to examine 
my shells when they arrived from Italy, and expressed 
my great desire to obtain his co-operation in my work, 
in which, as will appear in the sequel, I was fortunate 
enough to succeed. 
The preparation of my first volume had now been 
suspended for nine months, and was not resumed until 
my return to London in the beginning of March, 
1829. Before the whole was printed another summer 
arrived, and I again took the field to examine 'the 
Crag,' on the coasts of Essex, Norfolk, and Suffolk. 
The first volume appeared at length in January, 1830, 
after which I applied myself to perfect what I had 
written on 'the changes in the organic world,' a 
subject which merely occupied four or five chapters 
in my original sketch, but which was now expanded 
into a small treatise. Before this part was completed 
another summer overtook me, and I then set out on 
a geological expedition to the south of France, the 
Pyrenees, and Catalonia. 
On my return to Paris, in September, 1830, I 
