CHAZY LIMESTONE. 279 



ternal, central or external. This is a chambered shell, partially curved, in distinction from the straight 

 forms of the Orthocerata. 



Bucania. An undetermined species of this genus of mollusks was collected in Ferrisburgh. This genus 

 was proposed to include several species of shells of a peculiar form, usually referred to Bdleroplion, from 

 which they differ in having all the volutions visible. It is a convolute shell ; spire equally concave on 

 either side; volutions in the same plane, all visible, outer one ventricose, inner ones usually angulated on 

 the edge, concave on the ventral side; aperture rounded-oval, somewhat compressed on the inner side by 

 contact with the next volution, laterally and dorsally abruptly expanded. 



In the first volume of the Palajontology of New York, Prof. Hall describes a species of coral from 

 Vermont, near Granville, N. Y., under the name of Stidopora glomerata. A specimen is figured in that 

 volume, Plate IV, Fig. 5. It consists of a surface several inches square, covered and crowded with this 

 coral, completely denuded of its celluliferous crust. Its appearance is very similar to certain specimens of 

 S. fenestrata (Hall), though its mode of growth is considerably different. It was principally from this 

 circumstance, and the impossibility of defining the external characters of the coral, that it was referred 

 with some hesitation to a distinct species. The specimen came from a limestone containing Maclurea 

 magna, which establishes satisfactorily its position in the Chazy limestone. 



Upon Isle La Motte there are many layers of limestone, mostly made up of fragments of crinoidal 

 columns ; but no portions of the other parts of the animals. 



Among these crinoidal columns there are small rolled masses, in the shape of acorns or eggs, which 

 are referable to the genus Chcetetes. 



Geological Position and Equivalency. 



This rock is intermediate between the Trenton limestone and the calciferous sandrock 

 of the New York Survey. We give a section taken from Prof. Adams' Second Geologi- 

 cal Report, with his description, to illustrate its position :* 



Section across Larrabee's Point, Shoreham. 



"The accompanying figure (Fig. 178) represents a section across Larrabee's Point in Shoreham, with a 

 direction from north to south, one hundred and fifty rods long, and fifty feet high. The strata dip 10 

 north. a,a, level of Lake Champlain ; c, bluff of brown clay, overlying Trenton limestone, which has 

 been worn down to an even surface, and scratched by drift agency ; c, c, brown clay ; i, conformable junc- 

 tion in Judd's quarry of the Trenton limestone and Isle La Motte [Chazy] limestones, indicated by change 

 of fossils ; Favosites lycoperdon being common in the upper strata, and Maclurea magna occurring 

 less frequently in m, the lower beds. The upper are rather thin, but the lower beds are very thick and 

 compact, furnishing the black marble; n, thick-bedded limestone jointed ; o, thin slaty layers, with 

 slender fucoids abundant." The beds o, belong to the calciferous sandrock ; and thus the Chazy limestone 

 is shown in its usual position. 



We have noticed no mineral in this formation, except pyrites. Prof. Adams' notes mention the exis- 

 tence of this mineral in large quantities at Carlton's Prize, a small island at the southwest corner of South 

 Hero. Upon this island there is also some bog iron ore of inferior quality, that has probably been derived 

 from the decomposition of the pyrites. Under " UnstratifiedEocks," several dikes that occur in this form- 

 ation will be described with their constituent minerals. 



BIRDSEYE LIMESTONE. 



The next rock in the lower silurian series in New York, and elsewhere, is a peculiar 

 limestone of thirty feet thickness. It is generally a bluish or light dove-colored limestone, 



* See page 1G4. 



