GENERAL LAWS IN GEOLOGY. 593 



under which he comprehends all known kinds of 

 fish ; namely, the Cycloidean and the Ctenoidean ; 

 while the other two orders, the Ganoidmn and 

 Placoidean, rare in our days, suddenly appear 

 in great numbers, together with large sauroid and 

 carnivorous fishes. Cuvier, in constructing his great 

 work on ichthyology, transferred to M. Agassiz the 

 whole subject of fossil fishes, thus showing how 

 highly he esteeemed his talents as a naturalist. 

 And M. Agassiz has shown himself worthy of his 

 great predecessor in geological natural history, not 

 only by his acuteness and activity, but by the com- 

 prehensive character of his zoological philosophy, 

 and by the courage with which he has addressed 

 himself to the vast labours which lie before him. 

 In his Report on the Fossil Fish discovered in 

 England, published in 1835, he briefly sketches 

 some of the large questions which his researches 

 have suggested; and then adds 6 , "Such is the 

 meagre outline of a history of the highest interest, 

 full of curious episodes, but most difficult to relate. 

 To unfold the details which it contains will be the 

 business of my life" (D A). 



Sect. 2. Transition to Geological Dynamics. 



WHILE we have been giving this account of the 

 objects with which Descriptive Geology is occupied, 

 it must have been felt how difficult it is, in contem- 



6 Brit. Assoc. Report, p. 72- 

 VOL. III. 



