242 AMADEUS W. GRABAU 
Lake and other regions; and that these dunes were subsequently 
altered, by replacement, to iron ore. 
The series of limestones overlying this basal bed, or resting 
directly upon the Ordovicic, is for the most part richly fossiliferous. 
Some of the beds, as the Racine and the Coral Beds, are characterized 
by reefs of Stromatoporoids and other corals, widely distributed and 
connected by more or less barren lime sands (calcarenytes) which 
resulted from the erosion of the reefs. Some beds are of shallow- 
water origin and bear the marks of periods of exposure, resulting 
in the formation of mud cracks, etc. The fauna is more or less uni- 
form throughout, and the series represents continuous deposition, 
recording only minor oscillatory movements. Southward we find 
these beds extending through northern Illinois, Indiana, and Ohio, 
with a more or less uniform fauna, while further south, in the Cin- 
cinnati and western Tennessee regions, part of the limestones is 
replaced by shales and new faunal elements appear. 
The typical Niagaran jauna.—This is to be found in the strata 
of the Wisconsin section and in their continuations in northern 
Illinois, Indiana, Michigan, and Ohio. It is an exceedingly rich 
fauna, and, as Weller has ably demonstrated, has many elements 
in common with the Mid-European Siluric. The Stromatoporoids 
abounded on the reefs of the Coral Beds and the Racine. They have 
not been much differentiated in Wisconsin, but from other sections, 
especially Canada and Ohio, a considerable number of genera and 
species have been recognized. Corals abound, especially Halysites 
and Favosites, while Bryozoa are most common in the shales of 
New York and the southern area, Fistulypora making extensive 
reefs in western New York. The brachiopods, except the large 
Pentamerus, are likewise more characteristic of the shales. Crinoids, 
Cystoids, and Trilobites appear to be most common in the lime- 
stones of the interior. 
The Guelph jauna.—This fauna demands a_ special notice, 
because it is so distinct in its eastern manifestations. The peculiar 
aspect of the fauna is produced by the great Trimerelloid brachiopods 
(Trimerella grandis, T. ohioensis, Monomorella prisca, etc.); the 
peculiar corals Pycnostylus; the large pelecypod Megalomus canaden-. 
sis; the gastropods Pycnomphalus solarioides; and the genera 
