282 On the Structure and Position of Eozoon Canadense. 



belief lias been gradually gaining ground among geologists, 

 that all limestones have been originally formed by the agency 

 of Coral-polypes, Echinoderras, Mollusks, etc., -which fix carbon- 

 ate of lime from sea-water, just as plants fix carbon from the 

 atmosphere, the mere fact of the occurrence of a limestone 

 bed in strata otherwise non-fossiliferous, raises a presumption 

 that organic life had not been wanting, even at that very early 

 period. And it is to this epoch, represented in our own 

 country by the Lower Cambrian strata, that one of our ablest 

 and most experienced geologists, Professor Phillips, has re- 

 cently assigned the origin of life on the earth.* He points 

 out that in passing downwards through the Lower Paleozoic 

 strata, the forms of life grow fewer and fewer, until in the 

 lowest Cambrian rocks they vanish entirely, though these 

 strata are of a kind such as might be expected to yield them. 

 And the deficiency is not confined to the British types of the 

 series ; it is equally noticeable in their equivalents in North 

 America, in Norway, and in Bohemia — countries well searched 

 for this very purpose. "The absence is general; it seems due 

 to a general cause. Is it not probable that during these very 

 early periods the ocean and its sediments were nearly devoid 

 of plants and animals, and in the earliest time of all, which is 

 represented by sediments, quite deprived of such V The fol- 

 lowing table is given by him as showing the marked reduction 

 in number of types as we descend to the lowest beds of the 

 Lower Silurian, and thence to the Upper Cambrian ; this last 

 reduction involving the entire loss of the representatives of a 

 large proportion of the higher groups of mollusca. To com- 

 plete the table we add a line, in which are noted all the types 

 yet discovered in the Lower Cambrian. 













cS 





























































e3 

 O 

 N 

 O 



•a 

 o 



a 



O 

 PR 



o3 

 "ft* 

 O 



o 



03 

 1 



m 

 o 



c3 



S3 



03 

 O 



? 



o 



eg 



o 



N 



o 



P4 



03 

 O 



cf 

 o 



<3 



"S 



a 



o 

 p 



03 



"a 



a 

 p 



03 



o 



ft 

 o 



s 



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53 



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o 



ft 



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r-l 



<0 



e3 

 T3 

 O 



ft 



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 ft 



s> 

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Upper 



") Ludlow 

 j Wenlock 





1 



10 



17 



18 



39 



1 



30 



17 



41 



27 



4 



4 



30 



Silurian 



3 





6Q 



34 



6 



36 



25 



79 



12 



15 



18 



3 



3 



22 



Middle 

 Silurian 



> Llandovery 



2 



... 



26 



6 



3 



16 



5 



69 



5 



13 



26 



6 



3 



13 



Lower 



I Caradpc 



3 





23 



20 



8 



82 



27 



67 



7 



31 



25 



7 



7 



26 



Silurian 



3 Llandeilo 







4 





7 



34 



'22 



18 



1 



2 



3 



2 



6 



4 



Upper 

 Cambrian 



> Lingula 





... 



2? 





2 



11 



1 



3 















Lower 

 Cambrian 



> Longmjnd 



«_ 





2 





5 



1 











...j... 







* Life on the Earth ; its Origin and Succession. Cambridge, 1860. 



