44 CONTRIBUTIONS TO DEVONIAN PALEONTOLOGY. [bull. 244. 
COMMENTS ON SECTIONS. 
By H. S. Williams. 
The facts here presented are chiefly valuable for the statistics them- 
selves, viz, the detailed analysis of a number of local faunules. A word 
may be added, however, to indicate the bearing of these statistics upon 
the general problems of correlation, and upon the determination of the 
particular horizon to which each fauna should be assigned. 
On the ordinary basis of correlation (i. e. , the presence of species 
which have heretofore been recorded from some definite geological 
horizon) it is easy to indicate the general position of the several zones 
in the geological column. This general classification is indicated by the 
lettering of the separate parts of the sections which are arranged 
in approximately parallel order. (See sections, pp. 1@, 28, 43.) 
In this arrangement the capital letters O, S, R, D, and C are employed, 
with the following meaning: O indicates Ordovician; S indicates Silu- 
rian, not later than Niagara in age; R, the formation containing the 
Rensselaeria fauna, called Giles formation in the Pocohontas folio, Han- 
cock formation in the Estillville folio, the upper sandy portion of it 
being called Monterey sandstone on several of the Virginia and West 
Virginia sheets; D is used to indicate the Devonian formations as low as 
the Jeffersonville limestone of the Indiana survey; C indicates forma- 
tions in which Carboniferous faunas are recognized. 
On the east side of the Cincinnati arch there appears to be an uncon- 
formity at the base of the black shale. West of it (in Indiana, Ten- 
nessee, southern Illinois, and Arkansas) a limestone occasionally occurs 
conformably below the black shale. This limestone has a fauna which 
appears in the New York Onondaga limes tone, and sometimes it con- 
tains traces of the Tropidoleptus fauna of the Hamilton formation of 
New York. Where this limestone occurs the unconformity appears 
below it. 
There is considerable irregularity in the age of the formation 
immediately underlying the unconformity. In most of the western 
Kentucky and Indiana sections the underlying formation is Silurian 
and carries a Niagara fauna, but in some of the Kentucky sections, 
as well as in northern Arkansas, the highest formation below the 
unconformity is Ordovician. In the more eastern sections in Virginia 
and West Virginia the Rensselseria fauna is found in some of the 
uppermost Silurian formations immediately below the black shale. 
In western Tennessee, and also westward beyond Arkansas in Indian 
Territory,* traces of the Rensselaeria fauna also appear. 
It has not been definitely proved that there is an unconformity 
below the formation containing the Rensselseria fauna, but in both 
"Girty, G. H., Preliminary report on Paleozoic invertebrate fossils from the region of the McAlester 
coal fields, Indian Territory: Nineteenth Ann. Rept. U. S. Geol. Survey, pt. 3, 1899. 
