Upper Silii.ri((ii in yorfhea.sfcrn loini. — Wilson. '21^) 
THEUPPER SILURIAN IN NORTHEASTERN IOWA.* 
By A. (t. Wilson, Hopkiiitoii, Iowa. 
The literature on Upper Silurian t'oriuations in Iowa is not 
very extensive. In I). I). Owen's report of 1S40, relating to 
the mineral lands of Iowa, Wisconsin and part of Illinois, the 
Niagara formation and Galena limestone were classed together 
under the name of Upper Magnesian limestone. 
The Maciuoketa shales between the Niagara and Galena were 
not observed by Owen. The Cliff or Upper Magnesian lime- 
stone, however, he divides into the upper, middle and lower. 
As the middle and lower are said to be rich in lead and zinc, 
the upper must have been what is now- known as th(> Niagara. 
This is characterized as follows:! "More regularly stratitied 
and less frequently vertically tissured than the middle and 
lower, also more rich in siliceous fossils ; containing layers of 
chert and indeed passing sometimes wholly into masses of 
flinty rocks; containing also good iron ore and much crystal- 
lized carbonate of lime, but lead rarely and in unprofitable 
quantities." He says further that these upper beds contain 
casts of TerebratuUie, which, from his description and figures, 
appear to be Penfa merns <>hltiii<iiis Sowei-by,^ and various 
names are given for corals now known as //(ifi/.sifcs ciiletniJa- 
fiis Linn., Ptiichoplijill mn cx/xi usit in Owen, LiicIUk ijlnbra 
Owen, Stroinhodea nunn nii/aris Owen, 'SVyv>////;oJr\s' (/ii/as Owen, 
and various others. None of the Iowa reports since that date 
(except the reprint of this one in 1844) has figured any fossils 
from the L^pper Silurian. 
In Dr. Owen's much larger report in lHi)'2 on Wisconsin, 
Iowa, Minnesota and part of Nebraska, this Ui)pev Magnesian 
or Cliff limestone is passed over Without so much as a mention. 
In the ma]) accompanying this report, however, he called 
this terrane the Coralline and Pentamerus beds of the U]>per 
Magnesian limestone, indicating also tliat it is the ecpiiv- 
alent of the ('liiiton and Niagara groups of t lie l'i)per Silurian, 
while the lead bearing beds arc placed in the fiowcr Silurian 
in Ills tal)le of colors. 
In HalTs report on Iowa in iSoS three forniations arc de- 
scribed as representing the Upper Silurian, viz., the Niagara, 
*Read before Soetion E, A. A. A. S., Springfield. 189.'). 
tOp. cit., p. 24. 
JSee pp. GG, 121. 
