GRAPTOLITES OK NEW YORK, PART 2 6 1 



Likewise the Ardennes in Belgium and northeastern France have fur- 

 nished a series of graptolite zones beginning with the Upper Cambric 

 Dictyonema shale and leading up to the end of the Middle Siluric. 

 Smaller series which, however, are still remarkably long when compared 

 with those of the other facies, are formed by graptolite shales in the 

 Bretagne, Wales, the Normandy, Bohemia etc. 



The broad proposition can therefore be made that graptolite shales, as 

 a ride, are deposited in the same region for longer intervals than most ot her 

 fossilifcrons rocks; or in other words, that the conditions producing the 

 deposition of graptolite shales tend to persist longer in the same region than 

 those producing most other facies. The explanation for this fact can be 

 found only in the assumption that the regions of this shaly sedimentation 

 were more distant from the ever changing conditions of the higher litoral 

 zones than those of the other contemporary facies, i. e. were in deeper 

 water. This conclusion of the place of origin of the graptolite shales is in 

 full agreement with Lapworth's view that the graptolite shales represent a 

 zone between the agitated bottom, where coarser sediments are deposited, 

 and the dead water of the deep sea, with that of Barrois [1892, p. 174] that 

 the graptolite shales were deposited at depths corresponding to those in 

 which the radiolarian ooze is found 1 and with the writer's conception of the 

 mode of existence of the graptolites set forth in Memoir 7 [p. 509]. We have 

 there concluded that true graptolites were pelagic, the Axonolipa essen- 

 tially pseudoplanktonic and the Axonophora holoplanktonic in their mode 

 of life and that the latter from their structure must have preferred the 

 deeper and quieter regions of the open sea. 2 



'The distinguished French author bases his inference mainly on the great amount of 

 authigene silica (60%) in the typical graptolite shale, and especially on the intercalation 

 in them of phtanites which contain radiolarians and diatoms [Cayeux, Ann. Soc. Geol. du 

 Nord, 1891]. 



2 During the progress of this discussion the writer has been well aware of certain evi- 

 dence apparently conflicting with the view of the continuance of deeper water conditions 

 in the northern part of the Appalachian geosyncline. This consists of the observation of 

 the presence of intraformational conglomerates, as that described by the writer from Ryse- 



