96 [Senate 



scure; but the Black slate, which T regard as the continuation of the Marcellus 

 shale, occurs in the immediate neighborhood. The fossils are all found loose in the 

 bed of a stream, washed out by the water from the rock. The fossils themselves 

 are s'licified to a great extent, and the adhering stone is an impure or siliceous 

 limestone of light color and compact texture. In the vicinity of New-Albany and 

 Jefferson ville, Indiana, the Marcellus shale rests upon the limestone of the Falls 

 of the Ohio, which is a continuation of the Upper Helderberg limestone. In this 

 neighborhood, the Black shale ( Marcellus shale) is succeeded by a band of com- 

 pact fine-grained, and in some parts crystalline light-colored limestone, undistin- 

 guishable, in fragments, from that accompanying the Goniatites and other fossils 

 from Rockford. From all these facts, I have been inclined to regard the evidence as 

 favoring the view that these Goniatite beds of Rockford are near the horizon of the 

 upper part of the Black slate, the position of which maybe regarded as determined 

 with reference to the Marcellus shale of New-York. 



With these preliminary remarks, I will proceed to enumerate the fossils at pre- 

 sent known to me from these localities. 



GONIATITES EXPANSUS (Yanuxem). 

 Geological Report, Third District, 1842, page 146, fig. 1. 



Goniatites expansus and Goniatites marcellensis : Vanuxem, Geol. Report, Third District, 



1842, p. 146, f.2. 



Of the latter or Marcellus Goniatite ( page 147 ), Mr. Vanuxem remarks : 

 " This species is more abundant, and some are of great size. A fragment of one 

 " was found, which, when perfect, must have been nearly a foot in diameter. 

 " Both specimens are in the State Collection." 



Having been familiar with the original specimens figured by Mr. Vanuxem, and 

 with the later collections from the same neighborhood and from Schoharie, I am 

 compelled to regard them as one species, which, in all conditions, presents some 

 variety; but between the young and the old specimens, there are differences which 

 might well be mistaken for specific characters. The young are more rotund, and 

 are rounded on the dorsum, with a double groove and ridge between, along the 

 dorsal margins; the sides are strongly striate, with arching ridges. As the shell 

 becomes older, the back is less rotund, the grooves and rounded carinse along the 

 dorsal angles disappear, and the ridges on the sides become obsolete; the dorsum 

 is flat, and the angles are quite plain. So different indeed do they become, that it is 

 only when we dismember the parts and find the interior to correspond with the 

 G. expansum, that we feel satisfied that this species is only the young of the 

 G. marcellsnsis, which attains to such large dimensions and occurs very abun- 

 dantly; much more abundantly than the smaller one, the young, which is in some 

 localities comparatively rare. It is from the investigation of a large number of 

 individuals, and from having seen and collected them in the localities mentioned, 

 that I have arrived at this conclusion, and therefore feel compelled to unite these 

 two described species under the name of Goniatites expansus. 



The septa in this species are comparatively simple, and scarcely departing from 

 the nautiloid t3^pe. They are, hovv-ever, very distinctly lobed upon the back, and 

 have a dorsal siphuncle. 



The accompanying diagrams will illustrate the characters described. 



