286 Cincinnati Society of Natural History. 
shales are generally dark brown, blue and black, and the grits gray, 
greenish and bluish gray. They are stratified and conformable, alter- 
nating a great many times without any regular order of alternation. 
The thickness is about 800 feet. It has a wide geographical distribu- 
tion in Canada, and reaches a thickness of 2,000 feet. In the Lake 
Huron region it consists of a bluish or greenish colored argillaceous 
shale, holding thin beds of dark blue argillaceous, yellow-weathering 
sandstone; near the top there are marls, which are red, green, or a 
mixture of both: they hold very thin beds of dark bluish argillaceous 
limestone, the whole being surmounted by beds of gray or bluish aren- 
aceous limestone. The thickness on Grand Manitoulin Island is 200 
feet. In Ohio, Indiana and Kentucky, it consists of irregularly alter- 
nating layers of calcareous shale, marl and limestone. The thickness 
is about 800 feet, and the upper part is extremely fossiliferous. It 
occurs in Pennsylvania, Virginia, Tennessee, Missouri, Iowa, Texas, 
and New Mexico, and may be regarded as a universal group, though 
its petrological characters change, essentially, at distant localities. 
The fossils are, usually, remarkably well preserved and abundant, and 
we are, therefore, frequently able to identify species that commenced 
an existence in earlier groups. ‘There are many peculiar tracks found 
on the indurated shales supposed to have been made by Gasteropoda, 
Cephalopoda and Trilobites that have received such generic names as 
Asaphoidichnus, Trachomatichnus, Teratichnus, Petalichnus, Orma- 
thichnus, and Serichnites. 
The distribution of the other genera supposed to have commenced 
their existence in this group is as follows: 
In the vegetable kingdom, Blastophycus, Heliophycus, Dystacto- 
phycus, Dactylophycus, Trichophycus, and Sphenothallus, are peculiar 
to it. 
Among the Protista, Microspongia is peculiar to it. 
Among the Polypi, #istulipora, Zaphrentis, and Favosites pass up 
to the Carboniferous; Alveolites to the Devonian; Halysites, Helio- 
lites, and Sarcinula to the Niagara: Favistella to the Clinton; and 
Megaloyraptus, Dicranograptus, and Columnopora are peculiar to it, 
Among the Echinodermata, Protaster passes up to the Keokuk 
Group of the Subcarboniferous; Anomalocystites to the Oriskany; 
Lepadocrinus to the Lower Helderberg; Hemicystites to the Niagara; 
and Anomalocrinus, and Xenocrinus are peculiar to it. 
Among the Bryozoa, Cyclopora and Trematopora to the Subcarbon- 
iferous. 
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