in Western North America. 20 



This is a very good Ceratopyge fauna, and the presence 

 of Pelt ura is especially interesting. 



SUMMAEY. 



It appears that with the exception of Symphysurus, the 

 trilobites characteristic of the Ceratopyge fauna, such as 

 Ceratopyge, Apatokeplialus and Hemigyraspis are not 

 sufficiently abundant to be very useful as guide fossils, 

 although diagnostic when present. Among the brachio- 

 pods, Syntrophia nundina and Eoortliis desmopleura are 

 ubiquitous and easily identified, so that an association of 

 Symphysurus with these may be used as a guide to the 

 fauna. On this basis, it seems that the Ceratopyge fauna 

 occupies a position at the base of the Ordovician from 

 Robson Peak in Canada southward to the Eureka District 

 in Nevada, on the western side of the Rocky Mountains. It 

 is somewhat doubtful if it will be found in that part of 

 Montana east of the Continental Divide, but further south 

 it may extend across Xew Mexico and Texas to the Appa- 

 lachians, although no trace of it has yet been reported. 

 In the east it is known only in Pennsylvania, New Jersey 

 and Xew York, until the northeastern Atlantic coast is 

 reached. There seem more possibilities of a connection 

 across the southern than the northern part of the conti- 

 nent, however, judging from the distribution of the Beek- 

 mantown. 



One very important point is the notable admixture of 

 Upper Cambrian fossils found in the Ceratopyge zone, 

 especially in Nevada and the Mount Robson district. In 

 no case is there either physical or f aunal evidence of emer- 

 gence between Upper Cambrian and Lower Ordovician. 

 Richardson has outlined some physical evidence of an 

 unconformity between the St. Charles and Garden City 

 formations in the Randolph quadrangle in Xorthern 

 Utah, but since the upper part of the St. Charles has a 

 Ceratopyge fauna, and the lower part of the Garden City 

 a very similar one, the unconformity is in the wrong place. 



TTalcott 16 has tentatively suggested that the lower 

 Pogonip contains a representative of the "Ozarldan," 

 and has described CalvineUa tenuiscidpta, a member of 

 the Dikelocephalidae, stating that it was probably from 



10 Smithson. Misel. Colls., vol. 57, p. 359, 1914. 



