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most important alterations in the other classes of fossil 

 animals and vegetables, and also in the mineral condition 

 of the strata. Hence we find that the genera of fishes 

 which prevail in strata of the Carboniferous order, are 

 found no more after the deposition of the Magnesian Lime- 

 stone. Those of the Oolitic series were introduced after 

 the Magnesian Limestone, and ceased suddenly at the 

 commencement of the Cretaceous formations. The genera 

 of the Cretaceous formations are the first that approxi- 

 mate to existing genera. Those of the lower Tertiary- 

 deposits of London, Paris, and Monte Bolca, are still 

 more nearly allied to existing forms ; and the fishes of 

 Oeningen and Aix approximate again yet closer to living 

 genera, although every one of their species appears to be 

 extinct. Not a single species of fossil fish has yet been 

 found that is common to any two great Geological forma- 

 tions, or living in our present seas. In 1836, M. Agassiz 

 had determined upwards of 1,000 species of fossil fish, of 

 which about 400 were British, whose Geological distribution 

 approach somewhat to the following, — Silurian system, 5 or 

 6; Old Red Sandstone, 20; Coal Measures, 56; Magnesian 

 Limestone, 16; Oolitic series, 150; Green Sand and Chalk, 

 50 ; London Clay, 50 ; Crag, 5 or 6 ; since which period 

 the numbers are greatly increased, especially in the Old 

 Red Sandstone. 



Having dwelt longer than perhaps I am justified, in 

 introducing to your notice the value of fossil fishes, in 

 a Geological point of view, with their distribution, I must 

 now proceed to my analysis of the animal remains in our 

 own Coal Field. For the information of those who may 

 not have looked into the subject, I feel it necessary to 

 explain that the four orders under which the fish are classed, 

 is in accordance with the views of M. Agassiz. 1. The 

 Placoidians, 2. Ganoidians. 3. Ctenoidians. 4. Cycloidians. 

 Each of these orders existed during particular Epochs. Only 



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