The Age of the Galena Limestone. — WincheU. 37 
of the summarized facts, so far as they bear on the age of the 
Galena limestone. 
It was found that the Galena limestone changes gradually 
toward the north, by acquiring shale. While this seemed to 
pervade the entire limestone mass by the interbedding of 
scattered thin layers of shale at irregular intervals, yet it is 
most apparent, perhaps, near the bottom, where shaly charac- 
ters take the place of calcareous ones, on the same horizontal 
plane. Therefore as a lithological horizon there was no de- 
pendence to be placed upon it. It was found, also, that the 
fossils wiiich had been said to be characteristic of the Galena 
limestone in Iowa, occurred in some shales underlying the 
limestone. Paleontologically, therefore, the Galena limestone 
had not definite downM^ard limitation. In this absence of pos- 
itive stratigraphic characters, it became necessary, if the 
term be worth}-^ of preservation, to assume a horizon in the 
midst of the shales, below which the term Galena might not 
extend. This lower limit was chosen at the lowest position 
at which the characteristic ff)ssi]s, named by the authors of 
the term, were known to occur. Such fossils as Tschadites 
ioirensis, the sunflower coral of the lead region, and Clitain- 
bonites dirersa have here their first appearance. They are 
associated with an increased abundance of Zyyospira recnrvi- 
rostra, and with several species of Neniatopora and Arthocle- 
mn. At this horizon also occur Rhynchotrerna inequilcrdvis, 
Orthis pectinella (var. sii-eeneiji) and Pholidoj)s trentonensis 
(var. minor). Here also are found several species of Stropho- 
mena, viz, hillingsi, achojieldi and emacerata. Here was found 
a new species, Orthis ineed.si. Several others which are found 
first at lower horizons, occur here, apparently, in increased 
numbers, viz., liaiiffella Jtlosa, Cylindrovo'lia minnesofensis, 
Diastoporina Jfabellatifin, and Mitoclema miindidinii. 
Owing to the progressive change, both vertically and hori- 
zontally, from limestone to shales, in passing northward from 
the typical region of the Galena limestone, it cannot be said 
that the foregoing paleontologic characters will everj'where 
be found at any set lithologic horizon. But as an average, for 
the southeastern part of Minnesota, it is probably true to say 
that the base of the Galena formation is ft)und to occur about 
30 feet below the lowest distinctivelj' dolomitic beds. Toward 
