284 FOSSIL FISHES, 
Comparing the Fishes of the Chalk with those 
of the elder Tertiary formation of Monte Bolca, 
we find not one species, and but few genera, that 
are common to both.* 
Fishes of the Tertiary Formations, 
As soon as we enter on the Tertiary strata, 
another change takes place in the character of 
fossil Fishes, not less striking than that in fossil 
Shells. 
The fishes of Monte Bolca are of the Eocene 
period, and are well known by the figures en- 
graved in the Ittiolitologia Veronese, of Volta ; 
and in Knorr. About one-half of these fishes 
* It has been already stated, that the remarkable deposit of 
fossil Fishes at Engi, in the Canton of Glaris, are referred by 
M. Agassiz to the lower portion of the Cretaceous system. 
Many genera of these are identical with, and others closely 
approximate to, the fishes of the Inferior chalk (Planer kalk) of 
Bohemia, and of the Chalk of Westphalia (see Leonhard and 
Bronn. Neues Jahrbuch, 1834). Although the mineral cha- 
racter of the slate of Glaris presents, as we have before stated, 
an appearance of high antiquity, its age is probably the same as 
that of the Gault, or Speeton clay of England. This alteration 
of character is consistent with the changes that have given an air 
of higher antiquity than belongs to them, to most of the Secon- 
dary and Tertiary formations in the Alps. 
The Fishes of the Upper chalk are best known by the nume- 
rous and splendid examples discovered at Lewes by Mr. 
Mantell, and figured in his works. These Fishes are in an un- 
exampled state of perfection ; in the abdominal cavities of one 
species (Macropoma) the stomach, and coprolites are preserved 
entire, in their natural place. 
