6o NEW YORK STATE MUSEUM 



origin of their beds in deeper parts of the sea than most of the 

 fossiHferous rocks. This conception is found to be in full accord 

 with the views held by Suess, Neumayr and Haug in regard to the 

 deeper sea origin of the deposits in geosynclines and is also appli- 

 cable to the Paleozoic Appalachian geosyncline, as far as the Lower 

 Siluric era is concerned. The graptolite shales of the Appalachian 

 geosyncline reappear in Arkansas and the Indian Territory and 

 again in the Rocky mountains, but are absent in the vast intervening 

 area. These facts suggest that the Appalachian and Rocky moun- 

 tains geosynclines were connected in the south by a westerly bend of 

 the Appalachian geosyncline now buried in the Gulf of Mexico or 

 the Gulf States, a northern embayment of which is, however, still 

 exposed in Arkansas and the Indian Territory. 



A synoptic view of the genera of the graptolites of the United 

 States IS given. This brings out graphically the fact of three suc- 

 cessive culminating periods of the graptolites, each marked by the 

 appearance of a new group or order that has given to the class a 

 new lease of life by advancing to a new structure. The first of these 

 is the dichograptid culmination in the Beekmantown shale ; the next 

 the dicellograptid-diplograptid climax in the Trenton shale and the 

 last the monograptid culmination in the Siluric. The structural 

 and phylogenetic causes of these culminations will be made the 

 subject of a separate study. 



A separate chapter is devoted to the morphology of the spines 

 of the graptolites since these represent one of the striking features 

 of numerous forms. It is found that in the great majority of forms 

 the spines are placed distinctly on the most exposed parts in response 

 to stimuli from the environment. In many others (dwarfed phylo- 

 genetic forms) a general spinosity is clearly but an expression of 

 waning vital power and in a third important group, the most typical 

 representative of which is Glossograptus, a general spinosity is 

 ■produced by a tendency to repetition of the lateral spines commonly 

 found in any graptolite at the sicular extremity. In Lasiograptus 

 and related forms finally the spines were found to result from the 

 suppression of thecal structures caused by restraint of environment, 

 or in an endeavor to lighten the periderm. 



Another chapter was invited by the multitude of forms of the 

 appendages of the sicular extremity of Climacograptus 

 b i c o r n i s occurring in the Normanskill shales. It was found that 

 the several varieties based on the forms of these appendages are 

 all connected by transitions and represent one complex system mark- 



