232 Relation of Devonian Faunas of Iowa. — Williams. 
lying the Rockford shales at Rockford, Iowa, and recognized 
in Beaver Creek and Nora Springs, by Clement L. "Webster. 
(See, "A description of Rockford Shales of Iowa," Proc. Dav- 
enport Acad. Nat. Sci., Vol. V, p. 103, and note at bottom of 
pp. 103 and 104). Specimens of the fossil called Spirifera 
disjuncta Sow. by Mr. Webster, have been kindly sent for ex- 
amination by him, and I find them, not Spirifera disjuncta, 
but presenting the characters of the Spirifera mesostrialis 
Hall, of the Ithaca sandstone at the base of the Chemung 
group of New York, and also answering so closely to the de- 
scriptions of the Spirifera parry ana Hall, of the "yellow sand- 
stone" of Muscatine county, as to make it probable that S. 
parryana is but a western variety of S. mesostrialis of New 
York, in the same way that Orthis iowensis is but a western 
variety of the Orthis impressa of the New York faunas, both 
of which are but varieties of the European Orthis striatula 
Schlotheim. 
The zone in which Spirifera mesostrialis and Cryptonella 
eudora are characteristic in New York sections, is followed by 
the zone holding the fauna with Orthis impressa, Productella 
dissimilis Hall, and Rhynchonella pugnus Martin, of the 
geological reports of Illinois, {or= Rhynchonella alta^ of Cal- 
vin). 
Judging, therefore, from the order of succession of the 
faunas, which is beyond dispute in the Devonian of New York 
state and the Appalachians, it appears probable that the De- 
vonian fauna of Rockford, Iowa, and the northern counties of 
Iowa, represents a large stage of the middle Devonian, or an 
early stage of the upper Devonian of the New York sections. 
If the fauna of the "yellow sandstones" of Muscatine county, 
Iowa, were in the rocks of the Appalachian Devonian, we should 
unmistakably place it at the base of the "Chemung Period," 
in what is locally called the "Ithaca group," and using the 
same standards, the Rockford shale fauna of Iowa would be 
placed a little higher up, in the Ithaca group. Both would 
be decidedly in the lower part of the upper Devonian, entirely 
below the first appearance of the lowest representative of typ- 
ical Chemung faunas. 
The discovery of the clue to the order of sequence of the 
Iowa faunas was first announced in my paper above cited, and 
had I then known the stratigraphy of the Iowa Devonian as 
