322 
IOWA CAMBRIC SUCCESSION 
term might be advantageously extended in scope so as to take 
precedence over McGee’s later proposed name Oneota.^^ It seems 
most clarifying not to attempt this; but to drop the Minnesota 
term altogether and use the already widely adopted Oneota. 
In the early volumes of the present Iowa Geological Survey 
McGee’s usage of the title Oneota for the main body of the 
Cambric dolomite was extended to cover^^ the entire lower 
Magnesian limestone of Owen. A decade afterwards Bain went 
back to McGee’s original definition; while the geographic term 
Prairie du Chien was proposed to cover exactly Owen’s Lower 
Magnesian section. Calvin, who was always partial to Owen’s 
subdivision, naturally adopts at once the title Prairie du Chien. 
This author, however, was somewhat obesed because of his paleon¬ 
tological observations. In 1892, having had opportunity to ex¬ 
amine the local collections of fossils belonging to Mr. F. H. Luthe, 
then of McGregor, he ascribed the fauna thus obtained to the 
whole of the Lower Magnesian dolomite.*® Because, also of the 
strong Ordovicic aspect of the McGregor forms he was further 
led to remove all the Lower Magnesian beds from the Cambric 
section and include them in the next younger period.*’^ This pro¬ 
cedure was by no means a necessary consequence of his study. 
Now, none of the Luthe fossils were found in situ. All were 
taken from talus fragments resting under the brow of the high 
river clifif. Furthermore, as Mr. Luthe lately informed me, the 
collections came from cherty layers which characterize the upper¬ 
most layers of the cliff, and above a Thin sandstone stratum — 
Calvin’s New Richmond layer. So the faunal assemblage de¬ 
scribed by Calvin was not a true Lower Magnesian limestone 
fauna at all, but only that which characterizes a superior restricted 
portion of it. It was in reality the typical Shakopee phase. 
Out of the entire succession of Cambric beds of the Upper Mis¬ 
sissippi basin the two guide-horizons par excellance, are the thick 
main body of dolomite, or Oneota formation, and the Peter 
41 Eleventh Ann. Kept., U. S. G. S., p. 331, 1891. 
42 Iowa Geol. Surv., Vol. I, p. 21, 1893; also. Ibid., Vol. IV, p. 61, 1895. 
43 Bull. U. S. Geol. Surv., No. 246, p. 18, 1905. 
44 Geol. Atlas U. S., Folio 145, p. 3, 1907. 
45 Iowa Geol. Surv., Vol. VII, p. 194, 1907. 
46 American Geologist, Vol. X, p. 144, 1892. 
47 Iowa Geol. Surv., Vol. XVII, p. 192, 1907. 
