Report of the State Geologist. 15 



of the Cretaceous; Climate of the Tertiary; Climate of the Plio- 

 cene and Quaternary. 

 Chapter 5. Process of Fossilization. 



Conditions necessary for Fossilization / Fossilization of Ani- 

 mals / Fossilization of Plants. 



Graptolitidae. 



Mr. E. Ruedemann, of Dolgeville, has communicated a very 

 interesting and important paper on the Development and Mode 

 of Growth of the Genus Diplograptus, McCoy. 



This paper covers the author's detailed investigation of the 

 structure and mode of development of species Diplograptus pris- 

 tis, Hall. The observations are based upon material in a remark- 

 ably perfect condition of preservation, obtained from the Utica 

 slate of Dolgeville, ^N". Y. It is shown that these graptolites, 

 generally occurring as isolated stipes, were actually colonies com- 

 posed of a large number of such individual stipes, growing radi- 

 ally from a center. The structure of the central part of the 

 colony is shown to consist in, (1), a central floating sack or pneu- 

 matocyst, demonstrating that the colony was unattached; (2), a 

 verticil of spherical gonangia, within which are found masses of 

 young graptolites or siculae attached to a central axis; beneath the 

 gonangia are, (3), the radiately-arranged graptolite stipes attached 

 by long, bare extensions of the axial rod or virgula of each stipe. 

 The mode of growth of the stipe is such that the thecse or indi- 

 vidual cells are, in their normal position, directed inward. This 

 is due to the fact that the first theca forms at the distal extrem- 

 ity of the young stipe or sicula, and in all later growth the 

 increase in cells is at the proximal extremity of the stipe. The 

 siculse may either become wholly free of the present stock and 

 commence the growth of independent colonies or may remain 

 attached to the original stock. Some of them seem to always fol- 

 low the latter course, and hence successive generations of gonan- 

 gia give rise to the successive generations of stipes apparent in 

 every well-preserved colony. Individual siculae departing from 

 the parent, as soon as their independence is attained, are shown 

 to be provided with minute floating disks which eventually 

 become the pneumatocysts of adult colonies. The paper is illus- 

 trated with three plates of highly instructive drawings. 



