GRAPTOLITES OF NEW YORK, PART 1 489 



can be recognized over immense areas, has given to the graptolites their 

 well known reputation as reliable indicators of homotaxial beds. It is the 

 merit of Linnarsson, Tornquist and Tullberg in Sweden, and of Lapworth in 

 Great Britain to have brought into general recognition the fact of the possible 

 correlation of the graptolite beds in different regions, and of their subjection 

 to the general law of progress and development of the organic world, and 

 thus to have freed them from the bane of suspicion which the theory of 

 colonies, promulgated by Barrande, had brought on all correlation by 

 graptolites. 



The elaboration of the European graptolite faunas has shown that the 

 graptolites, in their development, have three times in succession changed their 

 plan of structure and thus produced three large divisions, by which also the 

 zones can be divided into three large stratigraphic divisions. These are that 

 of the deeper Lower Siluric, which is characterized by the Dichograptidae, 

 or uniserial forms without axis; the higher Lower Siluric, in ^vhich the 

 biserial forms with axes, the Climacograptidae and Diplograptidae, impress 

 their character on the faunas ; and that of the Upper Siluric, in which the 

 Monograptidae, the uniserial forms with axes, hold the field almost to the 

 exclusion of all other forms. 



Of these the two first divisions are well represented in the graptolite 

 fauna of New York. The faunas of the first are the subject of the present 

 memoir, while those of the second division, which find their typical 

 representation in the Normanskill fauna, will be treated in a succeeding 

 publication. The third division, so richly developed in many parts of Europe, 

 as Sweden, Grreat Britain, Bohemia and France, is hardly more than suggested 

 by a few species found in the Clinton shales. 



To the correlation of the North American graptolite horizons with the 

 European zones on one hand and with the standard formations of this State 

 on the other, but little attention has thus far been paid. The difficulties here 

 are of the same character as those "with which Nicholson, Lapworth, Marr and 

 others have had to contend in Great Britain, namely an indescribable confusion 

 of the beds by extensive orogenic movements of this part of the earth crust. 



