Geology. 429 
Taconic formation, as a lower member of the Primordial Zone, to which ~ 
the Potsdam sandstone peciieeneaen? belon 
hese lower slates in Georgia, Vt., have as already remarked, furnished : 
certain trilobites of primordial type which Mr. James Hall has described 
under the name of Olenus Vermontana and Olenus Thompsoni, though 
they are ih ge gt referred si Barrande ~ the genus wpa oxides. In 
r 
Laurentian rocks a coarse reddish sandstone holding Scolithus like that 
from the Primal sandstone of Pennsylvania. Resting upon this, and dip- 
ping gently southward, is a limestone in which none both Olenus Thomp- 
. Vermontana, with what appears to n Arionellus, pasties 
eae Capulus, and a large spirally marked ao) poscting ng Zaphren 
tis, These rocks, which evidently represent the Primordial Pee are 
overlaid ies others containing the characteristic fossils of pr Calciferous 
sandrock and the compound graptolites of the Quebec group. These 
primordia trilobites then overlie me sandstone with Scolithus, but as we 
ave elsewhere observed, that species appears unlike the Scolithus from 
the Potsdam of sabe Cha amplain, and should not be too.much relied 
Olenus beds of Bellisle. 
We have seen that Emmons, guided by a false notion of the age of the 
Green Mountain gneiss which led him to admit an inversion of the whole 
New York,—to the Hudson group. In this, as Barrande shows, Mr, Hal 
felt himself spenies by the authority of Hisinger, who in his great work 
on the fossils of Sweden, Lethwa Suecica, 1837, gives the succession of 
palzozoic sons in Sweden as follows in ascending order; 1. Fucoidal 
sandstone ; Orthoceratite — — Alum slates with Olenus ; 
4, Ar if slates with graptolites ee 
The Olenus slates, said 7 is singer > overlie the orthoceratite lime- 
stone, (corresponding to the Trenton,) M vr. Hall ee A regarded as 
the equivalents of the Hudson group, in which Olenus was to be looked 
for as a characteristic fossil, and hence the strata sontaining ‘ties trilobites 
* Mr. Barrande refers to three species of Dikellocephalus indicated by Dr. Bigsby 
as sm ier fg Potsdam of New York. It will be seen by referring to his me- 
Moir (Qua S Godt Soc, 1858, p. 339, com ared with p. 420,) that Dr. B, alludes 
only to he. en of these species as described by Owen in the Mississippi valley. 
