58 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
fossils are apt to retain in great measure the characteristics 
of the oldest Paleozoic forms as we now best know them. 
Neither are the fossils likely to serve in Pre-Cambrian questions 
the same stratigraphic purpose that they so long have else- 
where in the geologic column. On this account mainly the real 
significance of these forms already discovered is commonly 
overlooked; or their salient features as possible indices to re- 
gional stratigraphy are misinterpreted. For these reasons it is 
that there is such a wide divergence of opinion concerning the 
taxonomic ranks of the various subdivisions of these oldest sedi- 
mentaries. 
In arraying the oldest sediments, or those strata lying be- 
neath the commonly accepted base of the Cambric section, or 
Olenellus zone, with the younger rather than with the older 
part of the general sequence undue emphasis is manifestly 
placed upon certain assumed faunal affinities. This appears to 
be the chief reason why Dr. A. Rothpletz, for instance, would 
be inclined to include in the Cambric section the fossiliferous 
limestones of Steep Rock lake, north of Lake Superior 2 . In 
the Beltian section of Helena, Montana, the same observer is 
even less fortunate in his conclusions relating to the geologic 
age 3 because here he actually worked in recognized Mid- Cambric 
strata instead of Pre-Cambrian beds as he supposed, as is con- 
clusively shown by Dr. C. D. Walcott . 4 
Apparently influenced partly by the Rothpletz views Prof. A. 
C. Lawson 5 argues for drawing in the Lake Superior region 
the' basal line of the Paleozoic section at the horizon of the great 
plane of unconformity called by him the Epiarchean interval 
( Anianic-Selkirkic hiatus) ; and by severe restriction of the 
term Algonkian the latter is made co-extensive with Proterozoic. 
However, the Steep Rock Lake fossils, which are the oldest or- 
ganic remains known, occur far beneath the level of the break 
representing the “Epiarchean Interval,” and the Algonkian 
section thus restricted proves to represent an elapse of time 
equal to, if not vastly greater than, the entire Paleozoic era. 
So there are grave objections to assigning to such a superior 
succession of strata so inferior a taxonomic rank. 
2 Oral communication. 
3 Die Fauna der Beltformation bei Helena in Montana, pp. 1-46, Miinchen, 
1915. 
4 S'mithsonian Misc. Coll., Vol. CXIV, p. 259, 1916. 
5 Bull. Dept. Geob, Univ. of California, Vol. X, p. 18, 1916. 
