‘ITICA SLATE AND HUDSON=RIVER GROUP. : 267 
322. 3. GRAPTOLITHUS SECALINUS. 
Pu. LXXII. Figs. 2 a, 3, ¢. 
Fucoides secalinus. Eaton. 
— simplex. Emmowns, Tac. System, pag. 27, pl. 5, fig. 1. 
_— — Ib. Agr. Report, pag. 71, pl. 17, fig. 1. 
Stipe linear, elongated, narrowing towards the base ; width variable, from less than one 
line to one line and a half or two lines; axis usually obliterated, when preserved it is 
capillary like the preceding ; margins serrated, teeth more or less acute. 
This species is very closely allied to the preceding, if not identical with it, the difference 
being due to pressure and the extreme lamination of the parts. When we examine a species 
of this genus imbedded in calcareous matter, and trace the same in its changes presented 
in the slates of different character, we shall be ready to admit that the variable expansion 
or width is an unimportant character. I am therefore scarcely willing to admit this one as a 
distinct species. The slates of the Hoosick quarries have been more metamorphosed than in 
any other locality where we find these fossils ; they are more perfectly laminated, and the 
surfaces extremely smooth and glossy. If we can imagine them to have remained in a 
somewhat plastic state, and with these imbedded fossils to have been acted upon in such a 
manner that the surface has been extended or spread out, as is always true in altered slaty 
rocks, we can readily account for the greater expansion of the fronds of these graptolites 
without supposing them distinct species. 
In order to show that such a change may take place, I have introduced figures of 
specimens in the slate from Hudson and from Baker’s falls, where the rocks are partially 
altered and more regularly laminated than in the Mohawk valley, in order to show the 
gradual change which supervenes in the G. pristis under such circumstances. In these 
specimens, particularly in fig. 2 b from Baker’s falls, the substance of the fossil has almost 
totally disappeared, and is scarcely recognized, except by the difference of color in the 
surface of the slate. The same is always true in a greater degree of those from the 
Hoosick quarries, which are often so obscure that a particular direction of the light is 
necessary in order to distinguish the outlines of the fossil. To such causes, therefore, we 
may sometimes look for the foundation of species, particularly among forms like the 
Graptolites. 
Fig. 2a. A portion of the surface of a lamina of the Hoosick slate, with specimens of this fossil 
presenting some variations in character. The broader one crossing the figure has the form 
and appearance of Prionotus folium of Histnexr; but it is evidently only a more extenuated 
form of the same species as the more elongated and narrower ones. 
Fig. 2b, b. Fragments of the slate from Baker’s falls, with forms intermediate between the more expanded 
varieties of G. pristis and those from Hoosick. 
Fig. 2c. A specimen from Hudson, where the slates are partially metamorphic, but much less thinly 
laminated, and the fossils less expanded, than those at Bakeu’s falls or at Hoosick. 
34* 
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