STRATIGRAPHIC CATALOGUE. L'43 



It is quite manifest that there is a very marked irregularity 

 in the distribution of all fossil forms. While it is largely origi- 

 nal and real, it is in part only illusory. As in the modern sea 

 bottom, there are broad stretches where life is comparatively 

 infrequent; others where organisms are collected together in 

 great confused masses. Again, life is more abundant in some 

 zones than in others ; and at certain depths. Exposed places 

 are liable to be less frequented by animals than quiet, secluded 

 ones. 



The disproportion of numbers is readily comprehended in 

 a comparison between an almost unfossiliferous limestone and 

 one of the encrinital beds of the Lower Carboniferous, which 

 is made up almost entirely of the disjointed hard parts of 

 organisms, among which, however, are abundant remains of 

 only partially destroyed structures. When beds of this kind 20 

 or 30 feet thick and miles in extent are known, as in the case 

 of the Burlington limestones, it is perfectly inconceivable what 

 myriads of organisms must have flourished and died to supply 

 the material for such vast deposits. Very different is it with 

 strata many times thicker and far more extensive, yet contain- 

 ing ftot the slightest trace of ancient life. 



Granting the original prevalence of organisms in a given 

 area, diverse vicissitudes overtake the remains after they are 

 first entombed. Taking into account only those forms of life 

 which have hard parts sufficient to not immediately disappear 

 at death, relatively few traces ultimately remain. Percolating 

 waters remove the lime salts. Changes in the lithological 

 character of the rocks deform, disguise or obscure the 

 remains. When metamorphic action is intense all traces of 

 organisms are often completely obliterated. Thus, two 

 associated beds equally fossiliferous in the beginning may 

 become finally very different in this respect in the end. 



The sixth cause for disparity in the distribution of fossils 

 lies in the inherent capability of retaining their durability 

 through all the changes and accidents of time. Chemical 

 composition and character of the structures may be here men- 

 tioned. 



