500 NEW YORK STATE MUSEUM 



While the typical species of tlie zone with Di pi ograptus dentatus prevail, 

 both in number of species and individuals, thus characterizing the beds as belonging to 

 that zone, the congeries contains still a goodly number of species met only in the deeper 

 horizons at the Deep kill, namely, Goniograptus perflexilis, Tetragraptus 

 taraxacum and T. pygmaeus, Didymograptus filiformis and D. gra- 

 cilis. The Ashhill quarry beds represent hence a very early or initial phase of the zone 

 with Diplograptus dentatus not met with at the Deep kill, but whose existence 

 was surmised on account of the considerable break in the rock succession at that plaee.^ 

 The Dendroidea which constitute so large a portion of the fauna of the horizon at the 

 Deep kill are here represented only by a species of Ptilograptus and a few fragments 

 of a Dendrograptus ; but, as they also fail to be present in this zone in other countries, 

 they may represent but a local element. 



A notable feature of this faunule is the considerable number of species not observed 

 elsewhere, or in the preceding and succeeding horizons. Some of these forms, as 

 Didymograptus cuspidatus and D. spin osus, represent moreover peculiar 

 types and have no closely related congeners. Other species, as Diplograptus laxus 

 and Climacograptus pungens, which are new and very rare in the Deep kill 

 beds with Diplograptus dentatus, appear here in great profusion. These facts 

 characterize the fauna as constituting a distinct subzone of the zone with Diplo- 

 graptus dentatus. 



e Some general facts of distribution of graptolites [_see chart]. The 



specific identity of so great a percentage of forms in faunas characterizing 

 successive zones, as we find in the deeper zones of the Lower Siluric, over so 

 vast an area as that outlined above, by the notes on the distribution of the 

 Lower Siluric graptolites, is a fact without a parallel among the paleozoic 

 faunas. It has a distinct bearing on several problems, notably on that 

 of the mode of existence of the graptolites and of the distribution of land 

 and water in the Lower Siluric time. The former problem will be discussed 

 in the following chapter, the relation of the graptolites to paleography however 

 is still a virgin field, promising rich fruit after a most detailed comparison of 

 the various faunas. We can, with the present knowledge of the distribution 

 of the graptolites, do little more than make some general statements. 



i&e N. Y. state Paleontol. An. Rep't 1901, p. 573. 



