September 12, 1912] 



NATURE 



53 



The Cambrian Fauna of North America. 



The classification of the Cambrian fauna found in 

 North America is based on the researches of a band 

 of distinguished palEeontologists, comprising- among 

 the older investigators Billings, Hall, and Whitfield, 

 and among: modern workers Walcott, Ulrich, 

 Schuchert, Brainerd, Seely, Ruedemann, Matthew, 

 Clarke, and Grabau. Prominent among these inves- 

 tigators stands Dr. Walcott, alike for his original and 

 exhaustive contributions to this branch of inquiry and 

 for his complete mastery of the sequence and distribu- 

 tion of life in Cambrian time in North America. In- 

 deed, geologists all over the world owe him a deep 

 debt of gratitude for the services which he has ren- 

 dered to Cambrian paljeontology. 



Throughout the greater part of Cambrian time 

 there existed in North America two distinct life pro- 

 vinces. The eastern one ran along the Atlantic coast 

 from the north of Newfoundland to a point south of 

 New York, extending only a short distance inland, 

 with a faunal facies resembling that of north-west 

 Europe, exclusive of the north-west Highlands of 

 Scotland. The western province lay to the north-west 

 of that just described, and ranged from northern 

 Newfoundland, south-westwards to Central North 

 America and the Pacific Ocean. On the east side of 

 the Rocky Mountains it swept northwards to British 

 Columbia, perhaps as far as the Arctic Ocean. The 

 remarkable feature of the life of the western province 

 is its essentially American facies. 



Geologists are familiar with the triple classification 

 of the Cambrian S3"stem by means of the trilobites in 

 North America, as in Europe. The Lower Cambrian 

 division represents the OleneUtis epoch of \^'alcott, 

 characterised by some form of Olenellid, or, to use the 

 name now given to the family by that investigator, the 

 Mesonacidae. The western life-province contains the 

 true OleneUiis of which O. Tlwmpsoni is the type. 

 The strata yielding this fauna extend over such a wide 

 area of North America that within this same province 

 we find a western and an eastern facies. The western 

 facies is found in Nevada and California, where 

 Olenellus is represented by such specific forms as O. 

 Gilberti and O. Freemonti. But it is noteworthy that 

 these forms occur near the top of the Lower Cam- 

 brian series, and are soon followed bv Zacanihoides 

 and Crepicephalus, trilobites of Middle Cambrian 

 affinities. Towards the lower part of the sequence of 

 deposits, which there consist mainlv of limestone, and 

 extend downwards for a distance of more than 4000 

 feet beneath thp b^ds containing the true Olenellus. 

 Walcott found specimens of Holmia Rowei and Nevadia 

 Weeksi. The latter form is regarded by him as the 

 most primitive of all the Mesonacidae yet known. 

 Near the base the limestones have yielded the primi- 

 tive corals, Archaeocvathus and Ethmophvlliim ; and 

 the brachiopods Mickwitzia and Trematobolus. The 

 other forms found on this horizon belong to the fol- 

 lowing genera : (trilobites) Protypus and Micrndi^cus 

 (brachiopods) Ktitorgina, Smanfonia, Nisusia, Billins;- 

 sejla, and (tubicolar annelids) Hyolithelhis and 

 Saherella. The eastern facies of the western life-pro- 

 vince is best known from the region of Georgia, in 

 Vermont. It is the home of the type species of 

 Olenellus (O. Thompsoni). It is associated with 

 Mesonacis vermonfana, which has now given the name 

 to the whole familv, with Elliptocephahis asaphoides, 

 one of the earliest known trilobites of the family, and 

 with other forms such as Bathvnohis, Flolopygia, 

 Protypus, and Microdiscus. The tubicolar worms are 

 represented bv Hvolithellw! and .^alterella. the brachio- 

 pods by Nisusia, Swantonia, Kutorgina cingulala, 

 and Paterina lahradorica. There can be no doubt that 

 the assemblaee of organic remains found in this 



NO. 2237, VOL. go] 



Georgian terrane is merely the counterpart of that 

 found in the Olenellus zone of the north-west 

 Highlands. 



Proceeding now to the eastern life-province, we find 

 that the Lower Cambrian rocks are characterised by 

 the trilobite genus Callavia, belonging to the family 

 of the MesonacidcB, and bearing a close resemblance 

 both to Holmia and Nevadia. In southern Newfound- 

 land two species of Callavia occur, of which C. Brog- 

 geri is the t3'pe. It is accompanied by Microdiscus, 

 Hyolithellus, Paterina lahradorica, and Helenia bella. 

 In New Brunswick the Protolenus fauna, with Pro- 

 tolenus as the characteristic trilobite, probably repre- 

 sents the upper part of the Olenellus zone. In this 

 connection the recent discovery of the Protolenus 

 fauna bv Mr. Cobbold, in Shropshire, in strata asso- 

 ciated with Callavia, and overlain by beds yielding 

 Paradoxides, is of special importance, as it shows the 

 close relal,ion between the Lower Cambrian fauna of 

 Wales and that of the Atlantic or eastern province of 

 North America.* 



The Middle Cambrian division of the western life- 

 province is characterised chiefly by the trilobite genus 

 Olenoides ; indeed, the western part of it is the home 

 of Olenoides and the large-tailed trilobites. The char- 

 acteristic genera of this group to be found in that 

 region are Kootenia, Zacanihoides, Bathyuriscus, 

 Asaphiscus, Neolenus, Dorypygella, Dorypyge, Dame- 

 sella, and Ogygopsis. 



In this region the Middle Cambrian limestones and 

 shales occurring on Mount Stephen, in British 

 Columbia, have yielded a magnificent series of trilo- 

 bites, eurypterids, limuloids, Crustacea ranging from 

 congeners of the brine shrimps to phyllocarid nebalids, 

 annelids belonging to most of the still extant families, 

 holothurians, medusae, and other organic remains. 

 For the most part many of these forms are so fragile 

 that only their tracks remain as indications of their 

 existence in palaeozoic deposits. Not till we reach the 

 Solenhofen slates in Jurassic time do we find similar 

 favourable conditions for the entombment and pre- 

 servation of their highly modified successors. The 

 remarkable evidence bearing on the evolution of 

 groups of organisms furnished by this assemblage of 

 fossils from Mount Stephen has been admirably de- 

 scribed and illustrated by Walcott in his series of 

 papers published in the Smithsonian Miscellaneous 

 Collections. 



In the New Brunswick portion of the eastern or 

 Atlantic life-province the strata yielding Paradoxides 

 follow those bearing the Protolenus fauna. Six species 

 of Paradoxides have been obtained from this horizon, 

 including P. davidis, together with the following 

 genera : Agnostus, Agranlos, Lioslracus, Conocoryphe, 

 and Ctenicephalus. Schuchert points out that this 

 fauna is "closelv allied to the Paradoxides faunas 

 of Wales and Sweden, but less so with that of 

 Bohemia."' 



In southern Newfoundland Walcott showed that the 

 base of the Middle Cambrian division is marked in 

 Manuel's Brook by a conglomerate containing fossils 

 of the lower or Georgian terrane, thus indicating 

 elevation and erosion of the Lower Cambrian rocks. 

 Higher up the strata yielded Paradoxides davidis and 

 P. bennetti. 



Important evidence pointing to the conclusion that 

 the Paradoxides fauna of the eastern or Atlantic pro- 

 vince encroached to some extent on the eastern part 

 of the western life-province has been obtained by 

 Walcott at St. Albans, Vermont. But the suggestion 

 has been made bv Schuchert that their present posi- 

 tion is there due to north-westerlv thrusting.' 



liull. Geol. Soc. of An 



. (1910), p. 522, 



