1 2 Estimate of Temperature during the Tertiary Period^ 



following are the principal results, obtained by the aid of 

 considerable labour, which has occupied a great length of 

 time : — 



1. The tertiary strata of Europe contain no species which 

 can be identified with the secondary strata lying beneath 

 them. 



2. The tertiary strata are the only ones which contain 

 fossil specimens of existing species. 



3. The fossil shells which can be identified with living 

 species are more numerous in proportion as the strata are 

 more recent, and vice versa. 



4. Constant proportions (3 per cent, 19 per cent, 52 per 

 cent) in the number of recent species determine the age of 

 the tertiary strata. 



5. The tertiary strata are superposed one upon another, 

 and not parallel, as was at first imagined. 



6. The tertiary strata, according to their zoology, ought to 

 be divided into three groups, or stages.* The last of the ter- 

 tiary strata, those which lie nearest the surface, have been 

 deposited when the temperature of Europe was very nearly 

 similar to that which we experience ; as the following ob- 

 servations prove. The tertiary strata of that age, of Norway, 

 Sweden, Denmark, of St. Hospice near Nice, and of a part 

 of Sicily, contain in a fossil state all the identical species of 

 the adjacent seas, and, among others, those of which we have 

 already spoken, which, being more localised, serve best to 

 represent to us the temperature. 



In these fossils we remark the same series of varieties as in 

 the recent species, which indicates very decidedly an equable 

 state of temperature, or very slight modifications, from the 

 period when the fossils were buried there, until the present 

 day. 



These same strata, in France bordering upon the Medi- 

 terranean, Spain, Piedmont, Italy, Sicily, the Morea, and 

 Barbary, contain a great part of the species which live in the 

 Mediterranean; but contain, also, others of which the analogous 

 species either no longer exist, or are distributed in small num- 

 ber through the torrid regions of the Atlantic Ocean, and 

 through the Indian seas. To form a just idea of the tertiary 

 period upon the borders of the Mediterranean, we must re- 

 mark three kinds of fossil species : — 



1. Those of which the analogous species still exist in the 

 Mediterranean. 



* Since the month of August, 1831, when I proved the existence of 

 these groups, pointing out the places where they might he observed, ge- 

 ologists have confirmed their separation. 



