342 C. SCHUCIIERT MARINE INVERTEBRATE FOSSIL FAUNAS 



the correlation of formations, and that the greater half of the faunas will 

 radiate as far as the oceanic overlaps can spread over the continents. 



Faunal Provinces and Eealms 

 eattly paleozoic provinces 



Now let US turn to the marine invertebrate biotas and pick out some 

 of the Avell ascertained faunas, "to see how they group themselves into 

 realms and provinces. i\.t the ver)' beginning of the Paleozoic is Lower 

 Cambrian time, with its Avorld-wide Olenellus assemblages. In addition 

 to this genus, it is characterized by the perplexing Archaeocyathinse — 

 reef-making coelenterates, if such they are. In other words, we do not 

 see at this time clearly differentiated faunal provinces, but only one realm 

 common to all the oceans. 



In the Middle Cambrian, however, the faunal story is very different. 

 Now the world's marine waters are of two realms, a North Atlantic one, 

 with the trilobite genus Paradoxides, and a North Pacific one, with sev- 

 eral genera of large-tailed trilobites — the Bathyuriscus realm — common 

 to western North America and China. These large-tailed trilobites do 

 not get into North Atlantic waters until Upper Cambrian time. 



In 1863 James Hall described the Upper Cambrian biotas of Wisconsin 

 and Minnesota and acquainted us with many forms of trilobites, though 

 in a rather fragmented condition. Later, more genera and species were 

 added by other paleontologists, from Texas and the Eocky Mountains. 

 For a long time, however,. no faunal similarities with other continents 

 were seen, because of the slight knowledge then at hand relating to the 

 world's Cambrian assemblages. In 1883 the German paleontologist 

 Dames described a few Cambrian trilobites collected in eastern China by 

 Von Eichthofen, and for the first time directed attention to a faunal re- 

 semblance with those of the upper Mississippi Valley. Since then large 

 collections have been made in China by Blackwelder and Iddings for 

 Walcott, and now it is clear that in Middle and Upper Cambrian times 

 the North Pacific Ocean was a vast generating center of organic evolu- 

 tion. From it there spread great extensions of this ocean over eastern 

 Asia and aci»oss the United States, and in 1915 Walcott tells us that many 

 genera, either identical or closely related, are common to China, the 

 Eocky Mountains, Texas, and the upper Mississippi Valley. Not only is 

 there here this common faunal expression, but even the sequence of 

 Middle and Upper Cambrian ])iotas is alike on either side of the Pacific. 



One of the most rapid and widest dispersals of marine invertebrate life 



