PROGRESS OF ANIMAL LIFE. 115 
of the lower classes prevailed chiefly, at the com- 
mencement of organic life, but they did not 
prevail exclusively ; we find in rocks of the tran- 
sition formation, not only remains of radiated 
and articulated animals and mollusks, such as 
Corals, Trilobites, and Nautili ; but we see the 
vertebrata also represented by the Class of Fishes. 
Reptiles have been found in some of the earliest 
strata of the secondary formations.* In the foot- 
steps on the New Red sandstone, we have pro- 
bably the first traces of Birds and Marsupialia. 
(See PI. 26\ and 2(1.) The bones of Birds occur 
in the Wealden formation of Tilgate forest, and 
those of Marsupialia in the Oolite at Stonesfield. 
(See PI. 2. Figs. A. B.) In the midway regions 
of the secondary strata, are the earliest remains 
yet discovered of Cetacea.t In the tertiary forma- 
tions, we find both Birds, Cetacea, and terrestrial 
Mammalia, some referrible to existing genera, 
and all to existing orders. See PI. 1, fig. 73 — 101. 
Thus it appears, that the more perfect forms 
of animals become gradually more abundant, as 
we advance from the older into the newer series 
of depositions: whilst the more simple orders, 
though often changed in genus and species, and 
* E. e:. In the Magnesian Conglomerate of Durdham Down 
near Bristol, and in the bituminous marl slate, (Kupferschiefer) 
of Mansfeld in the Hartz. 
t There is, in the Oxford Museum, an ulna from the Great 
Oolite of Enstone near Woodstock, Oxen, which was examined 
by Cavier, and pronounced to be cetaceous; and also a portion 
of a very large rib, apparently of a whale, fr-om the same locality. 
