Ulrich—Paleozoic Systems in Wisconsin, 
93 
quent varying local migrations of the strandline during the early 
stages of the Franconia age. Abundant data indicating the char¬ 
acter and order of occurrence of these oscillations and the areas 
affected by them are available, but their citation and discussion 
would require more time and space than the present opportunity 
warrants. 
The Ironton sandstone member ,—Of the various members of the 
Franconia formation above briefly discussed only one is named on 
this occasion. The member so distinguished is the basal sand¬ 
stone of the formation in the southwestern quarter of the State. 
The Ironton sandstone member, as it is proposed to call it, has been 
recognized and studied at many places in Sauk, Richland, Vernon, 
La Crosse, Monroe, Jackson, Adams and Juneau counties. So far 
as observed in these counties the bed varies in thickness from 
about 2 feet to 12 or possibly 15 feet. At Ironton, the type local¬ 
ity, it varies from 5 to 10 feet. The top of the bed is even, the 
rapid inequalities in thickness being due to unevenness of its 
base. As a rule it forms the slightly hardened top of Dresbach 
sandstone bluffs and for this reason has usually been regarded as 
the terminal bed of that formation.^^ However, it is now quite 
clear and commonly accepted that it is of later date and, in fact, 
the initial deposit of the Franconia. 
The Ironton member is composed mainly of reworked washed 
and relatively coarse residual grains of Dresbach sandstone, the 
surface of which had previously been subjected to subaerial leach¬ 
ing and wear. The line of the break between the two formations 
—Dresbach and Franconia—lies at the undulating plane where 
washing and sorting of the loose quartz grains of the underlying 
formation is first indicated. In other words, the Ironton sand¬ 
stone member extends downward to the lowest plane indicating 
reworking and redeposition of the weather-loosened top sands of 
the underlying Dresbach formation. Commonly the new deposit 
includes a few grains of glauconite and other material that is not 
present in the undisturbed underlying beds of Dresbach sandstone. 
But to make sure of the identification of the Ironton member 
it is advisable to search for its characteristic fossils. In the 
Dresbach proper no organic remains—except perhaps worm bur- 
15 Twenhofel and Thwaites in their paper on the Paleozoic section in the Tomah 
and Sparta quadrangles, Jour. Geo., vol. 27, p. 616, 1919, apply the term “Wormstones” 
to relatively firm sandstone at the top of the Dresbach that may be a part of the Ironton 
sandstone member. 
