I'.IN li. S. WILLIAMS — THE CUBOIDES ZONE AND ITS FAUNA. 



Of their New York representatives, six are not known in the underlying 

 middle Devonian ( — T.)j &nd of the other tour, two are Bpecies common 

 below and above in both hemispheres, and the other two are more common 

 below in New York as well as in Europe. 



Review of the Argument. 



To review the arguments : the study of these faunas brings out the fol- 

 lowing facts. The fauna of the Tully limestone is made up of two groups 

 ofspecies; first, those having closely allied forms in the immediately preced- 

 ing middle Devonian formations; second, those having closer affinity with 

 European forms than with any species occurring in lower formations in 

 America. The first group may he regarded as representatives of indigenous 

 races and as direct descendants of the lower forms of the same region. The 

 second group must he regarded as immigrants from some other region. 



In the Tully limestone the latter class arc few, and they are species repre- 

 sented by very closely allied forms in the Cuboides zone of Europe, which 

 there were represented by preceding forms which were clearly their ancestors. 



In the Cuboides zone of Europe are a considerable number of species be- 

 side the few seen in the Tully zone. They all have unmistakable forerun- 

 ners in the formations preceding the Cuboid's zone in Europe and may be 

 considered as indigenous there. In America all of them follow the Tully 

 limestone zone, generally in the next or in some succeeding brachiopod 

 fauna, or else are first present in the Tully limestoue itself. 



This series of facts is explained by the hypothesis that during the early 

 stages of the Devonian period there was little or no communication between 

 the basin in which the American species were living and the European 

 basin, but thai near the opening of what is called in Europe the Ouboides 

 stage, communication was formed, and European Bpecies migrated and be- 

 came mingled with the eastern American forms; that the time of the ar- 

 rival here of the migrants was while the Tully lime-tone was being depos- 

 ited ; that the time when the migration left Europe WHS mar the time of 



deposition of the base of the ( iuboides /one ; that the correlation thus estab- 

 lished is one doI merely of hoinotaw, but within relatively BnOrl limits, of 

 contemporaneity ; and that the 'fully limestone may be said to have been 

 deposited during the period of deposition of the Ouboides Schichten of Eng- 

 land, Belgium, Pranci . Germany, Russia, ami the East. 



( \>N< II SION. 



'fhe conclusion we draw from this study of the faunas of the Ouboides 

 zone and the Tully limestone is that within vn narrow limits, geologically 



