GVlil THE PALEONTOLOGY OF MINNESOTA. 
most cases not distinguished, the species of the Bluff limestone and of the Vanuxemia 
bed being as a rule referred to the Trenton limestone or, more exactly, to the ‘‘lower 
limestone of the Trenton formation.” As we have said in discussing these beds on page 
xcii, their faunas are not greatly different. Still as the fossils from each are readily 
recognized in Minnesota by their modes of preservation,—those of the lower bed retain 
their shells while those of the Vanuxemia bed as a rule are casts merely—we have care- 
fully separated the species which, so far, appear to be characteristic of each. 
The greenish shales lying between the Vanuxemia bed and the yellowish or grayish 
shales of the Clitambonites bed were divided into three unequal parts or thirds, ‘‘ lower, 
middle and upper thirds of the Trenton shales,” corresponding in a general way with the 
Stictoporella, Rhinidictya and Phylloporina beds. The Ctenodonta bed is occasionally 
referred to as the ‘‘upper part of the middle third of the Trenton shales,” while the Fucoid 
bed is sometimes called the ‘‘ Orthis pectinella horizon.” 
The ‘‘ Prasopora insularis horizon” is the same as the Clitambonites bed, and it is this 
bed that is usually meant when the text refers a fossil to the ‘‘Galena shales,” though 
that term frequently also includes more or less of the Fusispira bed. As arule, however, 
the shales of the latter bed are distinguished as the ‘‘upper part of the Galena shales.” 
On the other hand, limestone deposits of the Fusispira bed in Fillmore county, the equiva- 
lents, of which in Goodhue county are referred to as Galena shales, are included with the 
rest of the Fusispira bed in the term ‘‘ middle Galena.’ In accordance with the sense of 
the last term, the Galena or Trenton group was divided into three lithologic divisions, the 
Galena shales, the middle Galena, a portion consisting principally of pure limestone, and 
the upper Galena or Maclurea bed, a magnesian limestone. 
The Maclurea bed alone maintains the typical dolomitic character of the Galena, but 
it diminishes in thickness from south to north, and may not have extended beyond 
Goodhue county. The lithologic changes in the strata have caused a slight overlapping 
in the designations of the special horizons. Thus the ‘‘Middle Galena,” in speaking of 
localities in Goodhue county, refers to the solid upper part of the Fusispira bed, while it 
refers to the whole of the bed when Fillmore county localities are mentioned. 
It is to be remembered that the Galena shale is merely a lithologic phase moving 
northward from county to county, and that it does not represent accurately any time 
interval in the Trenton at large, If studied only in the region between Cannon Falls and 
Berne the upper part of the shales would probably be separated as a distinct bed, as 
indeed was done by Sardeson who called it ‘‘Camarella bed.” But as this merges 
gradually into the rest of the Fusispira bed, both lithologically and faunally, there is very 
little reason, if any, for the sub-division. ; 
Occasionally reference is made in the volume to the Anastrophia bed, and the Upper 
Clitambonites horizon. These refer to shales in Goodhue county immediately over the 
Nematopora bed. It is the same horizon as the Platystrophia beds in Fillmore county, as 
that term is used in the 19th annual report. 
