No. 2.] THE PRIMORDIAL ROCKS OF TROY. 211 



Of these, six — OhoJclla (Avicula ?) clesquamata (Hall), 0. 

 (Orbicidaf) crrtHsa (H.), 0. {Orhicula) cadata (H.), Metoj)- 

 torria ri(gosa{H.), Theca trianguhti^is (R.), imd Agiwstus lohafus 

 (H.) — were fiu'ured and described in the first volume of the Pa- 

 Igeontology of New York in 1847, from this locality; and two — 

 ConoceplKiUtes {Atops) trillneatns (Emm.) and Olcndlus (EUip- 

 tocepludas) asaphoides (E.),* from Greenwich, Washington 

 county. All the rest are new or undescribed. f 



Desirins: further information in regard to certain of these new 

 species, I several months since wrote Mr. E. Billings, Palaeontolo- 

 gist of the Geological Survey of Canada, at the same time giving 

 him a list of the species in my possession from this quarter. In 

 reply Mr. B. informed me that he was just engaged upon a col- 

 lection of new fossils from the Lower Potsdam formation below 

 Quebec, which he strongly suspected to be identical with my own : 

 and on comparison it was found that fifteen out of the eighteen 

 species from Troy Avere held by us in common, and shown to be 

 perfectly identical. Such an unlooked-for result of course sur- 

 prised us greatly. That the Lower Potsdam formation below 

 Quebec, and the western portion of the Taconic series near Troy 

 are of the same age, there seems now but little room for doubt. 



Two very characteristic fossils of this formation are the oper- 

 cula of two species of IlijoJithes, upon which I communicated a 



* These two species, to which great interest has long attaclied, 

 were, until quite recently, supposed to be confined to an exposure of 

 the '' Black Slate" of Dr. Emmons, about two miles north of Bald 

 Mountain, N.Y., where they were first discovered by Dr. Asa Fitch of 

 Salem, N. Y., so long ago as the year 1844. Owing to the imperfec- 

 tion of the specimens furnislied by that locality, however, their tiue 

 relations have long been considered doubtful among geologists. But 

 the state of preservation m which they are now found in Innestone 

 leaves no longer a doubt as to tiieir true affinities. Good specimens of 

 these species are comparatively rare in the limestones at Troy, though 

 fragments of large individuals of the Olenelius asaphoides are very 

 common. I am indebted to Mr. Billings for having pointed out to 

 me the specific identity of the Troy speciiuens with the Afops and 

 Elliplocephalus — an acknowledgment which was unintentionally omit- 

 ted in this paper as originally published. As it is, however, about to 

 be republished in the " Xaturaltst and Geologist ^^^ I gladly i-mbrace this 

 opportunity to set the matter right. 



f Unless one of tliem should prove identical with the species of 

 Cypricardia figured by Kmmons (American Geology, p. 113, plate I, 

 fig 1.) 



