442 Br. H. Hicks — Life Zones in Palceozoic Hocks. 



appeared from the areas as depression went on, and though, as I 

 have already stated, there are some signs of a slight physical change 

 at the close of the Lower Cambrian, I believe that the main cause 

 why there should be no greater admixture of organisms, which 

 evidently were suitable to live under like conditions, was that the 

 fauna which first appeared, and which, to a certain extent, would 

 cling to the shores and occupy shallow basins, would pass on to 

 fresh areas as the depression increased.^ The tendency to migrate 

 along certain lines, and to follow like conditions, would undoubtedly 

 have a powerful influence with the organisms even at this early 

 period in the world's history, and many of the apparent difficulties 

 which crop up when an attempt is made to trace the order of 

 development will be brushed aside as Palseontology and Biology 

 join hand in hand more closely in these investigations. To my 

 mind no portion of the geological record can be more intensely 

 interesting to biologists than that which contains the history of these 

 earliest known organisms, as we have to deal only with marine 

 faunas with a comparatively limited number of types which, of 

 necessity, would be far less liable to be affected by disturbing 

 influences than land faunas. "When working out the Life History 

 in the Cambrian rocks at St. David's, I kept constantly in mind the 

 possibility of adding evidence in favour of the theory of evolution, 

 and as this could only be hoped for by the adoption of a minute 

 subdivision of the main Life Zones, I gave a section in my first 

 paper, published in the Proceedings of the Liverpool Geological 

 Society in 1863, showing five sub-zones in a thickness of 214 feet, 

 with names of all the genera and species found in each. At 

 this time the upper portion only of the Menevian (then called 

 Lower Lingula Flags) had yielded any fossils. Lower zones were 

 afterwards found and worked out on the same principle, and in the 

 year 1872 I was able to state that^ "the additions made to the fauna 

 of the Cambrian rocks by these researches include no less than 

 fifty-two new species, belonging to twenty-three genera. The 

 following table shows to what orders these belong, and in what 

 proportion they occur in these early rocks : — 



Trilobites 



Bivalve Crustaceans 

 Brachiopods 



Pteropods 



Sponges 



Cystideans 



10 genera including 31 species 

 4 „ „ 4 



4 „ „ 6 



3 ,, „ 6 



1 genus ,, 4 



1 „ „ 1 



genus, Frotolemis, -which, he says, is there the characteristic fossil of the Olenellus 

 zone {^' Vie-Faradoxides beds"). With it is associated the genus Ellipsocephalus, 

 which occurs in Europe in the Paradoxides beds, as well as in those containing 

 Olenellus (see Canadian Record of Science, October, 1892). 



^ Mr. C. D. Walcott, in his most instructive monograph "The Fauna of the 

 Lower Cambrian or Olenellus Zone," says, at p. 594, " The cause of the abrupt 

 change from the Olenellus to the Faradoxides fauna is not yet fully recognised. 

 "While a considerable portion of the genera pass up, very few of the species are 

 known to do so, and in none of the sections has there been found a commingling of 

 the characteristic species of the Lower and Middle Cambrian." 



2 Quart. Journ. Geol. Soc. vol. xxviii. p. 173. 



