184 F. W. SARDESON GALENA SERIES 



calcareous Maquoketa equivalent formerly gave rise to the report that tlie 

 Silurian— Niagara limestone extended into Minnesota, though it is really 

 absent there, the Devonian lying with unconformity on the Ordovician. 



By reference to faunal zones it can be shown also that the demarcation 

 between the so-called Trenton and the Galena has been drawn by authors 

 with great variance in differentt states and counties. The two forma- 

 tions, in short, had been recognized less uniformly over the entire area 

 than the uniform employment of the names Trenton and Galena would 

 imply. The extent of the variation appears in the scale and tabulated 

 references in the article already cited* and need not be discussed further 

 here. 



The Bbloit Formation 



The name Trenton limestone was brought into use in Wisconsin by 

 James Hallf in place of an older name. Blue limestone, on the theory 

 that this formation is the equivalent of the Trenton limestone of New 

 York. Hall also used at the same time the name Galena limestone for 

 the galena or galenite-bearing strata above the Trenton, the town of 

 Galena, Illinois, being presumably the type locality for this formation. 



The use of such a mixed nomenclatiire, partly local in origin and partly 

 from correlation with a distant, disconnected surface area, Avas never well 

 designed to avoid confusion of terms. That the Galena itself is largely 

 the equivalent of the New York Trenton limestone, while the so-called 

 Trenton of Wisconsin is not, must be now admitted as evident. J To the 

 problem which this mixed nomenclature presents either of two alterna- 

 tives offered a solution: The one was to use local terms only; the other 

 was to use exclusively exotic terms. I chose the former alternative in 

 1896,§ and accordingly proposed the name Beloit formation to replace 

 the name Trenton in this region. According to the then outlined plan, 

 the entire series of fourteen beds or faunal zones from the base of the 

 so-called Trenton (Beloit formation) to the top of the Ordovician in this 

 region divides into two series or groups the Galena and the Maquoketa. 

 The Galena series divides into Beloit formation and Galena formation. 

 Of the first nine faunal zones in ascending series the first five are com- 

 prised in the Beloit formation and the next four in the Galena forma- 

 tion. The tenth zone, that part of the limestone above the "cap rock" 



• The Galena and Maquoketa series, American Geologist, vol. xviii, 1896, p. 356. 



t Foster and Whitney's Report on the Geology of the Lake Superior Land District, 

 1851. 



t N. W. Winchell : American Geologist, vol. xv, 1895, pp. 33-39 ; R. D. Irving : Geol- 

 ogy of Wisconsin, vol. ii, 1877, p. 558. 



§ American Geologist, vol. xviii, 1896, pp. 360-361. 



