188 F. W. SARDESON GALENA SERIES 



number 5. The ''comjDlete section" at Platteville, as I saw it, extended 

 in partial out-crops along the river for several miles. 



U. S. Grant* describes the same section as Bain and adopts the name 

 Platteville limestone. Calvinf appears to be ready to adopt the same in 

 some sense, and the term Trenton is therefore evidently to give place to 

 some local name. None of these authors who have employed tlie name 

 Platteville limestone have made objection to or mentioned the Beloit 

 formation. We are left to our own resources to discover the relation 

 which the one may have to the other. 



Reference to the section above mentioned makes it evident that the 

 so-called Trenton as interpreted by Bain includes only the lower half of 

 what ChamberlinJ called Trenton in the south-central part of Wisconsin. 

 In searching for the authority for Bain's interpretation I find that his 

 description of the Galena limestone§ offers a clue to work on. He says : 



"It has long been known as the Galena limestone, a name applied by James 

 Hall to the beds in and around Galena, Illinois, and above the socalled Tren- 



tion."|| 



Hall describes the limestone at Platteville, at Galena, and at Dubuque. 

 Of the Trenton he says^f finally : 



"In all these localities the entire thickness of these lower limestones, which 

 can clearly be identified with the Trenton and associated limestones of the 

 east, is less than 50 feet ; but it is possible that some better exposure would 

 give a greater thickness." 



One might be deceived in Hall's meaning here if he forgot the fact 

 that Hall always quotes Orthis subcequata, Con., and associated fossils as 

 typical Trenton species. 0. subcequata, Con., proper belongs to the two 

 zones, 4 and 5, which appear to lie above Bain's section of the Platteville 

 limestone; and this limestone, which includes zones 1, 2, and 3, bear 

 0. perveta, Con., instead of subcequata proper. Of the Galena, Hall 

 says in the original description already cited (page 147) : 



"The principal fossil resembles a Coscinopora, but is probably a Receptacu- 

 Utes." 



Briefly stated, Platteville limestone is obviously synonymous' with 

 Beloit formation as to the intention to displace the so-called Trenton. 

 The term Platteville is not a "local name" in the sense of being applied 



* U. S. Grant : Economic Geology, vol. 1, 1905-6, p. 234. 



t S. Calvin : .Tournal of Geology, vol. xlv, 1906. 



t Loc. cit. 



§ Op. cit., p. 20. 



II Foster and Whitney : Geology of Lake Superior Land District, 1851, pt, 2, p. 146. 



H Loc. cit. 



