IOWA ACADEMY OF SCIENCE 
167 
THE SALEM LIMESTONE AND ITS STRATIGRAPHIC RELATIONS IN 
SOUTHEASTERN IOWA. 
By Francis M. Van Tuyl. 
While making a study of the Keokuk beds in southeastern Iowa during the 
field season of 1911, the writer was attracted by certain irregularities at 
the contact of those beds with the overlying strata. The Keokuk, insteaa of 
being followed always by the Warsaw, which is the normal order, was found 
to be succeeded above sometimes by a dense, white, fine-grained, non-fossil- 
iferous limestone, and sometimes by a fossiliferous magnesian limestone or by 
an arenaceous phase into which it grades laterally. 
The correct interpretation of this stratigraphic relation was reached only 
after many sections had been studied. It was found that the fossiliferous 
magnesian limesone and its equivalent arenaceous phase is a distinct forma- 
tion, and that the fine-grained, dense, non-fossiliferous limestone is the St. 
Louis. The fossiliferous magnesian formation or its equivalent has been, 
in places, completely eroded, permitting the St. Louis limestone to lie uncon- 
formably upon the Warsaw or Keokuk. A section in Henry county shows clearly 
that the fossiliferous magnesian limestone of this horizon is unconformable 
both with the St. Louis above and with the Keokuk below. 
It was thought at this time that the formation might be of the horizon 
of the Salem limestone of Illinois and Indiana, but as it was not then known 
by me that Weller^ ® had traced this terrane as far north as Hancock county, 
Illinois, considerable hesitation was entertained in drawing final conclusions. 
The fossils of the limestone were so poorly preserved that little use could 
be made of them in clearing up the difficulty. Subsequent perusal of the 
literature on the Salem and a trip to Warsaw to study the formation as 
described there by Weller has, however, led the writer to accept positively 
the conclusions which he had previously doubtfully entertained. Professor 
G. F. Kay, State Geologist, who visited the region recently, corroborates 
this interpretation. 
By earlier writers this formation has been variously classified and interp- 
reted. Hall included it with the Warsaw, but by Gordons KeyesS and Savage® 
it has been regarded as the basal member of the St. Louis. According to these 
writers the St. Louis limestone of the region embraces three units, namely, 
(1) a brown magnesian limestone characterized by the coral Lithostrocion 
canadense and sometimes grading into arenaceous layers, at the base; (2) vari- 
able beds consisting of dense gray limestone often brecciated and sometimes 
containing a bed of sandstone; and (3) a compact, thinly bedded, gray, 
fossiliferous limestone. By Bain® ^ these divisions have been designated the 
Springvale, the Verdi, and the Pella, respectively. The subdivision here des- 
ignated the Springvale has been made formerly to include the limestone which 
is now known to be of Salem age. The prevalent conception of many writers 
that the basal portion of the St. Louis limestone, which sometimes bears 
