_ trapsitions, either in the organic remains of the region, or in the 
aeaeodcion oa t . 
event in America was contemporaneous with a simi 
urope. The unity in geological history is in the progress of 
and in the great physical causes of change, not in the succes- 
n of rocks, 
_ iferous through the Cretaceous; III. The AGE or MAMMALS, 
_ the Tertiary and Post-tertiary; IV. The Acz or May, or the 
‘recent era;—/ishes being regarded as the highest and characterisic 
Ag the first age; reptiles of the second; and mammals of the 
-_ More recent researches abroad, and also the investigations of 
Prof. Hall in this country, have shown that the supposed fish re- 
Mains of the Silurian are probably fragments of Crustacea, if we 
SKS. 
ke the other two Invertebrate sub-kingdoms, the Radhate 
Articulate, : iest fossiliferous 
im oT 
tic size, 1 gt 
ilurian is therefore most appropriately styled the Mollus- 
Palzeozoic Trilobites belong to the lower tribe of Crusta- 
Crustacea rank low among Articulates. Moreover, Crus- 
(and the Articulata in general) did not reach their fullest 
velopment until the Human Era. ier : 
The Radiata were well represented in the Silurian periods; 
at, while inferior to the Mollusca as a sub-kingdom, only corals 
£2 
