DEVONIAN AND MISSISSIPPIAN FAUNAS 265 
shale. As regards the relations of these three formations Calvin says:’ 
“The three units referred to the Upper Devonian—the Sweetland 
Creek shales, Lime Creek shales, and State Quarry limestone—do not 
lie one above the other, but each is locally developed and lies uncon- 
formably on the Cedar Valley limestones.” 
The lower beds of the Wapsipinicon stage, other than the Inde- 
pendence shale, do not furnish any considerable fauna, Martinia sub- 
umbona being the most conspicuous species, but the higher beds, as 
well as the succeeding Cedar Valley beds, are abundantly fossiliferous, 
and faunally the dividing-line between the Wapsipinicon and Cedar 
Valley stages presents no more conspicuous break than that between 
the successive beds included within the Cedar Valley. 
In correlating these faunas of the Iowan Devonian with those of 
the Eastern Continental Province, difficulty is met with because of the 
few points of contact between the two faunas. The faunas in the two 
provinces are so distinctly different that we are forced to the conclusion 
that there could have been no free communication between the two 
regions, but that they must have been entirely separated during the 
whole or the greater part of Middle Devonian time by some barrier, 
probably a land mass. During Upper Devonian time there was much 
more in common between the Iowan and New York faunas, showing 
that communication had been established ere that time. In the corre- 
lation of the faunas in the two provinces the important point to deter- 
mine is the time of the establishment of this communication. Wil- 
liams? has shown that the Cuboides fauna of the Tully limestone in 
New York is a distinct immigrant fauna from the Eurasian province, 
probably by way of the Mackenzie Valley and Iowa. The character- 
istic species of this fauna is Hypothyris cuboides, a species which is 
represented in the Iowan faunas by Rhynchonella intermedia Barris, 
the Iowan form apparently being specifically identical with the New 
York species. In Iowa this species is limited in its range to the upper 
portion of the Wapsipinicon stage, where it is highly characteristic of 
one of the divisions of the Fayette breccia,3 and where it is associated 
with Gypidula comis. Because of the limited range of this species in 
tJour. Geol., XIV, 575; also Ia. Geol. Surv., XVII, 197. 
2 Bull. G. S. A., I, 481-500. 
3 Norton, Iowa Geol. Rep., IV, 160. 
