138 
SILURIC FORMATIONS IN MISSOURI 
1 
of the period elsewhere. The testimony of the fossils alone, as < 
recently set forth by Savage,^® is very far from being conclusive ' 
i 
on this point. A single criterion in correlation is entirely inade- , ; 
quate for the attainment of accurate results, or for the proper 
correction of the element of personal equation in the broader con¬ 
siderations of the subject. The field especially examined by the 
author mentioned is entirely too limited for broad deduction. 
With the Iowa rocks there is no careful comparison; and this is 
only a small part of the available field. Far to the north over 
the great Siouan arch traversing southern Minnesota,^^ and in 
Manitoba, the Iowa Siluric terranes find representation. / Until a 
greater array of facts to the contrary than those already produced 
is forthcoming it seems best to parallel the so-called Sexton lime¬ 
stone of northeast Missouri with the Goweran series of Iowa. 
Consideration of the diversity of the contained faunas is not 
without interest. Among the purely physical criteria which may 
be here mentioned are those of visiible continuity, lithological 
similarity, similarity of lithological sequence, unconformity, simul¬ 
taneous relations of diverse deposits to some physical event, com¬ 
parison of changes deposits have undergone from the action of 
geologic processes supposed to have been continuous, and the 
paleogeographical relationships. Even the biotic criteria now 
assume wider bearings than that which takes into account mere 
identity of fossil forms. , 
Probably the greatest shortcoming of the various considerations , 
of the fossil faunas characterizing the Siluric rocks of northeast 
Missouri is the marked insufficiency or lack of breadth in the 
treatment of the comparisons. This has led directly to the placing ; 
of undue emphasis upon the similarity of the faunal elements 
instead of their essential differences. One result is to throw to- i 
gether into a single limited series beds which other more reliable l 
and mutually supporting criteria indicate as belonging to three ^ 
great and distinct series covering the whole Siluric Period. The • 
common method of treating individual faunas tends to accentuate ^ 
the very points which it is most desirable to obliterate. Instead t 
of attempting the mergence of faunal characters it is the emphasis^ ^ 
of their diversity which is most needed if exact and permanent t 
results are attained. -j 
20 Illinois Geol. Surv., Bull. 23, p. 30, 1913. 
21 Proc. Iowa Acad. Sci., Vol. XXI, 1914. 
■J JS . 
