GKAPTOLITES OF NEW YOHK. I>AIt'r 1 469 



thecae or cellules. As to the mode of existeuce of the graptolites, Hall con- 

 cluded that the graptolites proper " in their mature condition were free floating 

 bodies in the Silurian seas." In regard to the genera Dendrograptus, Callo- 

 graptus and Dictyoneraa, he held that the frequent bulblike enlargements at 

 the base indicate attachment to bodies or an embedding in the mud. Even at 

 the present opinions in regard to the mode of life of the graptolites are greatly 

 at variance, and the problem has apparently not yet been solved to general 

 satisfaction. 



The introduction to the Graptolites of the Quebec Group, somewhat 

 enlarged and Avith the addition of supplementary notes on certain genera, has 

 been reprinted under the title, "Introduction to the Study of the Grap- 

 tolitidae," in the 20th annual report of the New York State Cabinet [1868J. 

 This publication closed Hall's work on the graptolites. 



In tracing the subsequent development of our knowledge of the grap- 

 tolites, it will greatly facilitate the grasp of the subject if we keep apart two 

 different trends of investigation. As the graptolites not only became interest- 

 ing and important as a class per se, which invited investigation by its early 

 extinction, the great variety of forms displayed and the ignorance of their 

 internal structure among paleontologists, but were also recognized as the most 

 reliable and widely distributed index fossils for the determination of horizons 

 of the Upper Cambric and Siluric, their study has been pursued from the 

 standpoint of the biologist as well as from that of the stratigrapher. 



We will first take up the investigations of the stratigraphic relations of 

 the graptolites, as these attracted the attention of numerous geol'r'gists long 

 before their biologic aspect. This work had naturally to begin with the 

 descriptions of the faunas found in the rocks of various regions. It can be 

 claimed that Barrande and Hall laid the foundations of this branch of the 

 science by describing the graptolite faunas of Bohemia and eastern North 

 America. At the same time, however, the exploitation of the graptolite 

 schists of Scotland, northern England and Wales had been undertaken by 

 the well known pioneers of British geology, among whom we enumerate 



