586 



GENERAL VIEW OF ZOOLOGICAL SEQUENCE. 



differ little from those of the coal measures, we cannot examine even that formation, 

 still less pass onwards through the overlying red sandstone and marl without perceiving, 

 that in the Sauroids of those days, we are surrounded by entirely new types of animal 

 life, which conduct us by almost imperceptible gradations into the period of the Am- 

 monites and Belemnites ♦ and as we enter among those groups, we take leave of many 

 of the generic forms, such as Goniatites, Orthoceratites and Producti, which abound in 

 the older periods. Lastly, in the tertiary system which links on the ancient deposits 

 with our own, we entirely lose sight of many of the former types, and are introduced 

 to a series of animal forms much resembling those which are now in existence. — Such 

 is the vast succession with which geology has made us acquainted 1 . 



I have now only to observe, that in the following plates and their descriptions the 

 organic remains are for the most part figured in the order in which they lie in the strata, 

 a method by which the chronology of the subject is strictly maintained. Every fossil 

 which occurs in more than one formation, is figured as belonging to that in which it is 

 most abundant, and its repetition in other strata is explained in the text and lists. 

 If naturalists should criticise this distribution, they will I hope excuse me when they 

 consider, that my great object is to record perspicuously a geological succession. 



Of the zoological department I have now to state, that the fishes are described by 

 M. Agassiz ; the mollusca and conchifers by Mr. J. de C. Sowerby ; the corals by 

 Mr. Lonsdale ; the crustaceans by myself. I have further to mention with gratitude, 

 that in various points of illustration I have been materially aided by Mr. Broderip, and 

 that Professor Phillips, Mr. C. Stokes, Dr. Beck, Dr. Milne Edwards, and Mr. Konig 

 have also contributed their assistance. The support, therefore, of such eminent natu- 

 ralists must have greatly augmented the value of this division of the work. 



the almost total absence of plants in the Silurian strata scarcely entitles me to enter upon this field of inquiry. 

 It is, however, fair to state, that two or three plants, said to be species well known in the carboniferous strata, 

 have recently been found in certain rocks of North Devon (considered to lie far below the culm or coal mea- 

 sures), and therefore as old, at least, as any portion of the Silurian System. If these data be eventually sus- 

 tained, they will only compel us to suppose, that the changes in the physical state of the bottom of the sea, 

 which produced the variations of its marine inhabitants, did not of necessity cause a change in the vegetable 

 forms of the land ; because the submarine operations may have exercised little or no influence upon aerial con- 

 ditions or climate ; and hence it may eventually be demonstrated, that the changes in animal and vegetable life 

 do not continue to run parallel to each other beneath a certain limit in the order of the strata, or in other 

 words during the earliest sedimentary accumulations. I confess that (judging from the analogy of the younger 

 deposits) I at one time held a different opinion; but if the evidences above alluded to are substantiated, I have 

 no difficulty in comprehending the rationale of the case. 



1 Although the stratigraphical order is strictly maintained in the collocation of the plates, the description 

 sometimes embraces a class or family in the same chapter. — Thus the Trilobites of all the Silurian strata, de- 

 scribed in Plates 7, 7 bis, 14, 23, 24 and 25, occupy one Chapter. 



