266 GEOGNOSY OF THE APPALACHIANS. [XIII. 







their organic remains, the fossiliferous Taconic rocks are shown 

 to belong. 



Mr. Billings has, it is true, distinguished provisionally what 

 he has designated an upper and a lower division of the Pots- 

 dam, and has referred to the latter the Red sand-rock with the 

 Olenellus slates of Vermont, together with beds holding similar 

 fossils at Troy, New York, and along the Strait of Bellisle in 

 Labrador and Newfoundland ; the upper division of the Pots- 

 dam being represented by the basal sandstones of the Ottawa 

 basin and of the Mississippi valley.* In the present state of 

 our knowledge of the local variations in sediments and in their 

 fauna dependent on depth, temperature, and ocean currents, 

 Billings, however, conceives that it would be premature to assert 

 that these two types of the Potsdam do not represent syn- 

 chronous deposits. 



The base of the Champlain division, as known in the Pots- 

 dam formation of New York, of the Mississippi valley, and 

 the Appalachian belt, does not, however, represent the base of 

 the palaeozoic series in Europe. The Alum slates in Sweden 

 are divided into two parts, an upper or Olenus zone, and a 

 lower or Conocoryphe zone, as distinguished by Angelin. The 

 latter is characterized by the genus Paradoxides, which also 

 occupies a lower division in the primordial palaeozoic rocks of 

 Bohemia (Barrande's stage C), the greater part of which are 

 regarded as the equivalent of the Olenus zone of Sweden and 

 the Potsdam of North America. The Lingula flags of AYalrs 

 belong to the same horizon, and it is at their base, in strata 

 once referred to the Lower Lingula flags, that the Paradoxides 

 is met with. These strata, for which Hicks and Salter, in 

 1865, proposed the name of the Menevian group, are regarded 

 as corresponding to the lower division of the Alum slates, and, 

 like it, contain a fauna not yet recognized in the basal rocks of 

 the New York system. [Beneath the Menevian lie the Llan- 

 beris and Harlech rocks (the Loiigmynd), which constitute the 

 Lower Cambrian of Sedgwick ; while above it are the great 

 mass of the Lingula flags and the Tremadoc rocks, his Middle 



* Report Geol. of Canada, 1863-66, p. 236. 



