PLATTEVILLE LIMESTONE 189 



to a single outcrop or within one county or state. The name Platteville 

 has been introduced without reference to the already published and de- 

 fined name Beloit formation. It is defined, as I think, without regard 

 for the geologic conditions at its type locality. It is also based upon a 

 wrong interpretation of the so-called Trenton and ignores the faunal 

 distinction which earlier founders of the Galena and Trenton forma- 

 tions sought to establish. 



The Platteville limestone appears to be designed to include the rem- 

 nant of the series or group when the Galena limestone is extended 

 downward to cover all the dolomitic or Galena phase of these rocks. It 

 is evidently based on a lithologic distinction. The basing of the forma- 

 tional unit directly and indirectly on lithologic characters in the Galena 

 series is worth further consideration. 



The formational Unit 



There seems to me to be a growing tendency, especially on the part of 

 of the directing geologists, to base the distinction of formational units on 

 lithologic rather than on faunal-floral evidence. The tendency in this 

 direction in many instances seems so marked as to be called a policy. In 

 case of the Galena series, the results of the two methods can be made to 

 compare and to show how the use of lithologic evidence, as generally 

 made, leads to confusion. While I am not disposed to blame the entire 

 existing confusion to lithology, the necessary difficulty which arises from 

 the lithologic formational unit seems worthy of full consideration. 



In this connection attention should be paid also to the very recent 

 article, "Notes on the geological section of Iowa," by Calvin,* in which 

 the question of confusion in connection with the use of the terms "Tren- 

 ton" and "Galena" are briefly discussed. After referring in this article 

 to an earlier discussionf of the "confusion which has arisen" and "the 

 probable causes of such confusion," he says finally : 



"Lithology and not stratigraphy was the basis of that classification. It is 

 now proposed to use the term Galena for all the strata above the 'Green 

 shales,' whether they are dolomitic, as at Dubuque, or are non-dolomitic, as 

 along the river at and above Decorah" [Iowa]. 



Again: 



"Bain's name 'Platteville' is acceptable for the beds below the top of the 

 'Green shales.' " 



While Calvin thus recognizes the erroneous way, he yet appears 

 bound — by usage, perhaps — to follow it. While he appears to rebuke 



* Samuel Calvin : The Journal of Geolosy, vol. xiv, 1906, p. 573. 

 t Samuel Calvin : Iowa Geological Survey, vol. x, 1900, p. 402. 



