﻿150 O. D. Walcott — Cambrian System of North America. 



Adamsi appears to pass up into the Potsdam horizon of the 

 section, where the fauna is more like that of the Potsdam; and 

 of the other species, Orthisina Orientalis is much like 0. Pepina 

 of the Potsdam sandstone of Wisconsin ; but the fauna, as a 

 whole, is so clearly distinct from the typical Potsdam of New 

 York, Wisconsin, Tennessee, Alabama, Texas, Arizona, Nevada 

 and Montana that, even without any section to show their rela- 

 tions to each other, I should not think of correlating them as 

 contemporaneous faunas. 



The stratigraphic relations of the Middle Cambrian fauna to 

 the Paradoxides fauna of St. John, Braintree and Newfound- 

 land are not so clearly proven as for the Middle, and Upper 

 Cambrian faunas. The only locality known where the two 

 faunas are in the same geographic area is about Conception 

 Bay, Newfoundland. At Topsail Head about 100 feet of 

 limestone is exposed, overlaid by dark shale. All stratigraphic 

 connection with other sections in the vicinity is broken. The 

 fossils in the limestone are not numerous, but Mr. Billings pro- 

 nounced them Potsdam (Geol. Newfoundland, p. 158, reprint 

 of report for 1868), and identified Salterella, Crania (probably 

 Kutorgina) Labradorica, and I found, in the collection of the 

 Geological Survey of Canada, Scenella reticulata, Stenotheca 

 rugosa, Iphidea bella and Protypus senectus var. parvulus, which 

 gives six species that are also known from the Middle Cam- 

 brian horizon of L'Anse au Loup.* Special stress is placed by 

 the writer on the occurrence of these fossils at Topsail Head, 

 as it is in the midst of the Paradoxides basin. Mr. Alexander 

 Murray correlated the Topsail Head limestone with that of 

 other localities, and places it beneath the Paradoxides-bearing 

 shales of St. Mary's Bay (on the page cited above), but without 

 paleontologic or stratigraphic evidence that can authorize him 

 to say more than that a supposed connection is indicated. 



Not having stratigraphic evidence of the relation of the 

 Georgia or Middle Cambrian fauna and the Paradoxides or 

 Lower Cambrian (Ordovician) fauna other than that they occur 

 in the same area and are not in the same stratum of rock, we 

 turn to the faunas to aid us in the settlement of the question. 



Of the thirty- two genera of the American Paradoxides hori- 

 zon, fifteen pass up into the Olenellus horizon, viz : Arenico- 

 lites, Protospongia, Archaeocyathus?, Eocystites ? ?, Lingulella, 

 Acrotreta, Acrothele, Kutorgina, Orthis, Stenotheca, Hyolithes, 

 Agnostus, Microdiscus, Solenopleura, and Ptychoparia. Of 

 these, eleven, Arenicolites, Protospongia, Lingulella, Kutorgina, 

 Acrotreta, Orthis, Hyolithes, Stenotheca, Agnostus, Microdis- 

 cus? and Ptychoparia, continue on up into the Potsdam or 



* Mr. Billings called all the Middle Cambrian fauna " Lower Potsdam," which 

 explains his referring the Topsail Head fossils to the Potsdam. 



