1889.] Description of the Devonian Rocks of Iowa. 241 
Platystoma lineatum. 
Ambocoelia umbonata. 
Productella truncata. 
Aside from the foregoing enumeration, we have in our cabinet, 
large numbers of undescribed forms. Two-thirds or more, of the 
species which constitute the fauna of this horizon, are not icnown, 
at present, to occur outside of it. 
When species, common to the shales, occur in any of the rocks 
below, and when fossils, peculiar to the lower groups, extend up- 
ward into the shales, they usually appear under a form, so altered 
that specimens from the different formations may be distinguished 
as readily as if they were distinct species. 
About one-third of the species of the upper shale fauna occur in 
other divisions of the Devonian of this area, as well as most other 
areas of North America ; and very closely allied forms also occur 
in the European strata of this age (see description and figures of 
fossils in the geology of Russia and the Ural mountains etc.; also 
Walcott's Monograph, Palaeontology of the Eureka District, U. S. 
Geological Survey, 1884, and U. S. Geological Survey of Fortieth 
Parallel, Vol. IV ; as well as a paper by H. S. Williams, " On a re- 
markable Fauna at the base of the Chemung group of New York," 
American Journal of Science, February, 1883). 
For a more detailed description of this formation, and its fau- 
nas, reference may be made to the following preliminary reports, 
which appear in various numbers of this Journal for 1888. " Notes 
on the Rockford Shales," and ** Description of new species of 
Fossils from the Rockford Shales of Iowa," also " Contributions 
to the knowledge of the Genus Pachyphyllum," and " Description 
of new and imperfectly known species of Brachiopoda from the 
Devonian rocks of Iowa ; " as well as to a paper on " A description 
of the Rockford Shales of Iowa." which is accompanied by a map 
of the area occupied by the shales, that appears in Vol. V. of the 
Proceedings of the Davenport Academy of Science. 
From the description of this formation here, and in previous pre- 
liminary reports, it will be seen in reality, to constitute a new and 
distinct group of strata, carrying two rich and varied faunas ; but 
which has not heretofore been recognized as such, and which is 
not developed in any other area in North America, or Europe ; al- 
though ail contain links of evidence which demonstrate its Devonian 
age. 
