PLATTEVILLB LIMESTONE 187 



Platteville is a new formational name which Bain is proposing for the 

 so-called Trenton. 



"Since tlie lithographic character has usually been relied on in discriminat- 

 ing the two, the line between them has been drawn at diffei-ent horizons in 

 va:rious parts of the region, and from north to south crossed the stratigraphic 

 horizons diagonally." 



The introduction of a proposed new formational name gives still 

 further significance to the work of that author on the Galena series. On 

 page 18 appears the following words : 



"Platteville limestone. — The beds included under this name have long been 

 known in this district as the Trenton limestone. Since it is now believed that 

 they are not the exact equivalents of the Trenton in its type locality, It is 

 proposed to use a local name for them. The formation is typically exposed in 

 the vicinity of Platteville, Wisconsin, and its entire thickness may be seen 

 along Little Platte river west of that town. The beds are largely made up of 

 non-magnesian limestone. In the lower portion are certain magnesian beds • 

 which are distinguished from the dolomites of the Galena by their earthy ap- 

 pearance. The Platteville limestone ordinarily has a total thickness of 60 

 feet while extremes in thickness run from 40 to nearly 75 feet." 



He then gives a generalized section, which incidentally shows the 

 Platteville in Illinois to be from 56 to 80 feet thick, as follows : 



Feet. 



4. Thin beds of limestone and shale 10-20 



3. Thin-bedded brittle limestone, breaking with conchoidal fracture.... 25-30 

 2. Buff to blue magnesian limestone, heavy bedded, frequently a dolomite 20-25 

 1. Shale, blue 1-5 



Numbers 1 to 4 are then discussed in some detail, in general agreeing 

 well with previoiTS descriptions of the buff rock, glass rock, and at least 

 part of the brown rock* already cited. 



T am somewhat familiar with the "complete section" along the Little 

 Platte river at Platteville and find some difficulty in believing that Bain 

 is right in saying that the Galena lithologic phase is found in rock rest- 

 ing on top of the section above cited. I can remember also having had 

 some difficulty with the stratigraphy there. On one side of a ravine by 

 the roadside was the rock and index fossils of zone number 3 and a little 

 way across the same ravine, at the same horizon, was quite the same 

 brown rock with index fossils of zone number 5 in it. Except for the 

 index fossils, I should have suspected no stratigraphic deception and 

 concluded that the Galena rested on the lower bed (3), instead of bed 



* J. D. Whitney : Geology of Wisconsin, vol. 1, 1866, p. 152. 



