288 



THE GEOLOGIST. 



Mr. Sharpe, because it harmonizes very well with my views on the 

 subject. 



I, NoETH America. — Potsdam Sandstone. 



Professor Hall only cites two Lingute and the ScolitJius linearis 

 here. Professor Rogers is said to have found a Discina. Sir C. Lyell 

 speaks of something resembling a Placuna. The profiles given by 

 D. D. Owen (see Eep. on Wisconsin, Iowa, &c., p. 499, &c.), cite 

 Lingula and Discina in the deepest beds, and the first other genus 

 appearing is Orthis. 



The Galciferous sandstone does not show any marked difference in 

 the character of Brachiopoda. Vanuxem and Hall only speak of a 

 Lingula found in a loose block. Bigsby mentions L. oMusa and 

 Ortliides here. 



The Ghazij limestone, on the contrary, contains ten species of Bra- 

 chiopoda (according to Hall), one single doubtful one, Orhicida {?) 

 deformis, belonging to the shallow water group A, the rest having 

 opaque shells, and only embracing one single Orthis. 



The Birdseye limestone contains no Brachiopoda, according to Hall. 

 The statements of Dr. Bigsby seem to be somewhat contradictory 

 (Quart. Jour., 1858, p. 431 and lists.) 



The Trenton limestone seems to form a great exception, and to con- 

 tradict all these statements in containing at the same time a great 

 number of species both of group A and of group B. Still, in 

 gathering the facts relative to the recurrence of these species in the 

 overlying strata, it may be shown that no contradiction exists. In 

 comparing the lists of Brachiopoda from the Trenton limestone, Utica 

 slate, and tludson river group, as I intend to do now, it is, I fear, 

 necessary to omit those given in Dr. Bigsby's lists with the authority 

 of Sharpe, because Sharpe united these three strata under the 

 denomination of blue limestone of Ohio, and the species named by him 

 in this bed are cited with his authority as B in exevj one of the 

 three strata. The following species are said to rise from the Trenton 

 limestone into the Utica State, and as no new species of Brachiopoda 

 appears in the State, they form the whole of the species found in it* : — 

 Hi>iri>j<'riua reticidaris, JRJiyncJionella increhescens, B. -niodesta, B. hidcn- 

 /(ila,, SI ropliom.cna alternata, Orthis lynx, 0. tcstudinaria, Bingida 

 ohtusa, L. curta, L. ovata, L. quadrata. The proportion is much more 

 in favour of group A here than in the Trenton limestone. In com- 

 paring the Hudson river group, you will find in it : — 



a, Species found in Ti'enton limestone, but not in Utica State : 

 Bingida crassa, OrtJiis TuUieiisis. 



h, Species passing indifferently through all three strata : Sjnri- 

 gerina rcficidn r/>!, lilnpirli. iiirrchc'^cciis, B. modesta, B. hidentata, 

 Stroj.}h. aJteruidd , Orlhis lynx (/), 0. tcstudinaria. 



* Mr. Hall's list cites Lcjpt. sericea hero for the first time. 



