NOTES ON THE GEOLOGICAL SECTION OF IOWA 573 



nesian of Owen into three units, here named respectively the Oneota, 

 New Richmond, and Shakopee. In the earHer reports of the Iowa 

 Survey the term "Oneota" was used as the full equivalent of the 

 Lower Magnesian of Owen. 



The St. Peter sandstone needs little comment further than to say 

 that McGee, in his Pleistocene History of Northeastern Iowa, extended 

 the application of the term downward so as to make it include the 

 Shakopee and New Richmond of the Lower Magnesian stage. It 

 was assumed that the two sandstones are related, and the inter- 

 vening Shakopee hmestone is only an incident. Apart from the 

 fact that they are made of quartz grains, the two sandstones have 

 nothing in common. The New Richmond hes in thin beds; the 

 surface of the beds is often ripple-marked; the individual grains, 

 in the most perfect way imaginable, show secondary enlargement; 

 some parts of the formation have been converted into a fair quality 

 of quartzite. None of these things characterize the St. Peter. 



The Platteville and Galena limestones. — The confusion which 

 has arisen in connection with the use of the terms "Trenton" and 

 "Galena" as apphed to certain Ordovician hmestones of the mid- 

 western states, and the probable causes of such confusion, are dis- 

 cussed in the "Geology of Dubuque County," in Volume X of the 

 Iowa Geological Reports. The assemblage of strata covered by 

 the two names conjoined is divided by a persistent band of shale 

 and shaly limestone carrying Orthis snbaequata and O. tricenaria 

 of Conrad as characteristic fossils. This band has been called 

 the "Green Shales" in some Minnesota and Iowa reports. All the 

 beds above the "Green Shales" are dolomitic at Dubuque, and, 

 so far as concerns this locahty, they have been consistently known 

 as the Galena limestone ever since the publication of the report on 

 the Geology of Iowa by James Hall in 1858. In locahties where 

 these beds are unaltered hmestones, they have usually been spoken 

 of as Trenton. Lithology, and not stratigraphy, was the basis of 

 the classification. It is now proposed to use the term "Galena" 

 for all the strata above the "Green Shales," whether they are dolo- 

 mitic, as at Dubuque, or are non-dolomitic, as along the river at 

 and above Decorah. Bain's name, "Platteville," is acceptable 

 for the beds below the top of the "Green Shales." 



