GRAPTOLITES OF NEW YORK. PART 1 501 



It has been pointed out by Freeh [1897, 2 :88] that for the lower and 

 middle Lower Siluric the existence of four grand marine provinces can be 

 inferred, which were more or less separated from one another. These 

 are the Bohemian-Mediterranean, the Baltic, the North Atlantic, and the 

 Pacific-North American basins. The former existence and extension of these 

 provinces is deduced from the comparative study of the horizontal distribu- 

 tion of the faunas, specially of their trilobite element. 



The graptolites, however, are expressly excepted as passing beyond the 

 boundaiies of these basins. Indeed, we find, for instance, the Tetragraptus 

 zone with its principal forms developed in the northwestern (St Lawrence) 

 and northeastern (British) embayments of the north Atlantic basin, in the 

 Baltic basin (Scandinavia), Bohemian-Mediterranean basin (southern France) 

 and Pacific- American basin (province of Victoria, Australia, and Nevada), 

 The same, with some exceptions, is true of the succeeding zones, at least as far 

 as the Trenton or Normanskill fauna is concerned. 



This phenomenon is explained by Freeh by their pelagic or abysmal 

 habitat in contrast to the littoral or shallow sea habitat of the provincial 

 faunas, which consist essentially of brachiopods, mollusks and trilobites. We 

 shall see in the succeeding chapter that, whatever may have been the mode of 

 existence of the graptolites, for various reasons they can not be considered as 

 having been littoral benthonic forms living in association with the representa- 

 tives of the other classes mentioned, but were . either pelagic or abysmal 

 organisms. Either of the latter are, today, notable for the vastness of the 

 territory inhabited by them, many of the former and nearly all of the latter 

 being cosmopolitan. 



While, however, the most common and characteristic species of the 

 graptolite zones appear also to be practically cosmopolitan, a closer comparison 

 of those liomotaxial faunas which have been thoroughly studied, brings to 

 light certain differences in the composition of the faunas which may 

 indicate divisions of the open sea, independent of those suggested by the 

 shallow sea organisms. We find in the Upper Cambric Dictyonema 



