336 The American Geologist. June, i89o 
"Geological Age. — The fossils contained in this formation, together 
with its position in relation to the underlying and overlying formations, 
leave no doubt as to the propriety of referring it to the same geological 
period as that in which the rocks at Cincinnati, Ohio, were formed; 
but as a formation, it is regarded as distinct from any other one of that 
group hitherto defined ; — the designation 'group' refers to a whole 
period in geologic time, and when it is applied to any single formation, 
its indefiniteness differs only in degree from a mere reference of tlie 
formation to its proper system or age. Therefore, as the strata of this 
formation, all referable without doubt to a single epoch of its period, 
are well developed on the Little Maquoketa river, where its character- 
istic fossils are also abundant, the name Maquoketa Shales is given to 
this particular formation of the group." 
Dr. White upon the authority of Messrs. Meek and Worthen 
and upon the strength of his own observations, rejects the 
term Hudson River group as applied to these shales in Iowa, 
Illinois and other interior states, and adopts the term Cincin- 
nati group instead, using, he says, "the name Maquoketa 
shales to designate that particular epochal sub-division or 
formation of the group which alone is found in Iowa. 
"Fossils. — Several species of fossils which characterize the Cincin- 
nati group are found in the Maquoketa shales, such as Orihis testudi- 
naria, 0. occidentalis, Strophomena alternata, S. (Leptsena) sericea, etc, 
but they contain a large number of species that have been found no- 
where else than in these shales in Iowa. They belong to the genera 
Orthoceras, Murchisonia, Pleurotomaria, Schizodus {?), Discina, Grapto- 
lithus, etc., The distinct faunal characteristics presented by these fossils 
last referred to, seem to warrant the separation of the Maquoketa shales as 
a distinct formation from any others of the group? Its true position is 
probably at the base of the group." 
It is thus seen that Dr. White considered this division of 
rocks as a distinct formation mainly for the reason that cer- 
tain species were confined to the typical locality. The force 
of this supposition will be considered under the discussion of 
the fossils. 
Having thus given the description which accompanied the 
original proposal of the name, let us examine the literature 
which deals with these or rocks of similar age as found in 
Iowa, in Wisconsin and in Illinois. 
The first detailed notice we find of the formation in geologic 
literature is by professor James Hall. In 1858^ he published 
a description of the rocks as observed by him in Iowa, under 
the name of the "Hudson River group." After noticing the 
connection between the Trenton and the Galena limestones, 
mention is made of the Hudson River group and its charac- 
ters in New York, Canada and Pennsylvania. Toward the 
^These last italics mine. (J.) 
■'Geol. Survey of Iowa, vol. 1. part 1. pp. 64-70. 
