PREFACE. XV 



studied for six weeks in the museum of M. Deshayes, 

 examining his collection of fossil and recent shells, 

 and profiting by his instructions in conchology. As 

 he had not yet published any of the general results 

 deducible from his valuable collection, I requested 

 him to furnish me with lists of those species of shells 

 which were common to two or more tertiary periods, 

 as also the names of those known to occur both in 

 some tertiary strata and in a living state. This he 

 engaged to do, and we agreed that the information 

 should be communicated in a tabular form. After 

 several modifications of the plan first proposed for the 

 Tables, we finally agreed upon the manner in which 

 they should be constructed, and the execution was 

 left entirely in the hands of M. Deshayes, in whose 

 name they were to appear in my second volume. 



The tables were sent to me in the course of the 

 following spring (1831), and additions and corrections 

 several months later. They contained not only the 

 information which I had expected, but much more, for 

 the names of several hundred species were added, as 

 being common to two or more formations of the same 

 period, whereas it was originally proposed to insert 

 those only which were known to be common to two or 

 more distinct periods. Thus, for example, more than 

 50 shells are now included in the tables, on the 

 ground that they are common to the tertiary strata 

 both of the London and Paris basins, although they 



