PHYSICAL AND FAUNAL EVOLUTION 6i 



ship is, accordingly, that of a progressively overlapping transgres 

 sional series to its basal bed, and this is the interpretation favored 

 by all the sections. The Chazy was, in fact, characterized by a 

 transgressive or positive diastrophic movement throughout (barring 

 possible minor oscillations), and therefore only the higher beds are 

 found in the region of late submergence. The thickness of the 

 formation beneath the Black Ri^'er, forms in general a reliable guide 

 to the division of the Chazy represented, though of course there may 

 be discovered some minor disconformities which would vitiate 

 detailed correlations made on this basis in a given region. 



No unquestionable Chazy beds have been reported from the Pacific 

 region, where the Trentonian seems to rest directly upon the Eureka 

 quartzite in Nevada, and either Siluric or Devonic succeeds the 

 Ogden quartzite of the Wasatch, with Mississippic beds succeeding 

 the same in the Uintas. The west coast transgression was, therefore, 

 less pronounced, the Nevada region remaining still uncovered at 

 the end of Chazy time (see map, Fig. 7). If Chazy beds occur in 

 the West, they must be sought for in western Nevada and California. 

 It is, of course, impossible to say how much has been removed by 

 late Ordovicic erosion. It is not improbable that the Chazy extended 

 east of Eureka, Nev., but was removed again in Upper Ordovicic 

 time. 



The Chazy fauna. — At the beginning of Chazy time, the Cham- 

 plain gulf was entirely distinct from the Appalachian gulf, there 

 being a land connection between the Laurentio-Mississippian con- 

 tinent and the united Appalachia and Taconia, or Ancient New 

 England continent (see map. Fig. 3). The faunas were thus to a large 

 extent distinct, representing, in fact, the Atlantic and the southern 

 type. The southern type was, in general, the Stones River type of 

 fauna; the character of which may be seen by consulting published 

 lists. The Atlantic type is seen in the fauna of the Champlain basin, 

 which admits of a threefold division, a lower (Div. A) with Orthis 

 costalis; a middle (Div. B) with Maclurea magna) and an upper 

 (Div. C) with Camarotoechia plena. 



That these two types of faunas were not wholly distinct in middle 

 and later Chazy time is shown by the occurrence of true Champlain 

 species of Mid- Chazy age, including Maclurea magna in the middle 



