No. 1.] GIBSON — GEOLOGY OF HURON COUNTY. 39 



limestone forms the fundamental rock of the district, may be 



accounted for, partly by powerful denudation during the upheaval 



of this area from the sea-bottom, and partly by the south-eastern 



dip of the strata. Here the beds are replete with fossils in a 



more or less silicified condition, the more important species being 



as follow : — 



Zoophyta. 



Fistulipora Canadensis^ Billings. Favosites Basaltica, Goldfuss. 



Favosites Goihlandica, Goldfuss. 3Iichelinia convexa, D'Orbigny — the 



hemispherica, Shumard. large cell openings being eatire- 



Sifringopora 3Iaclurea, Billings. ly silicified in most instances. 



Jlisiufferi, Billings. Eridophyllum Simcoense, Billings, 



Zaphrentis prolifica^ Billings, and species of the following 



gigantea. genera : Fhillipsastrea, Clisio- 



Heliophyllum Eriense. phyllum^ Diphyphyllum and Cy- 

 Catiadense, Billings. stiphyllum. 



Brachiopoda. 



Orthis Livia^ Billings. Stricklandia elongata^ Billings, for- 



Strophomena rhomboidalis, "Wahlen- merly Pentamerus elongatus of 

 berg. Vanuxem. 



a?npla, Hall. Atrypa reticularis^ Linna?us, also 



Streptorhynchus Pandora, Billings. occurring in the Wenlock lime- 

 Rhynchonella Thalia, Billings. stones of Great Britain, in 



Pentamerus aratus, Conrad. Sweden, Bohemia and in the 



Spirifera duodenaria, Hall. Ural Mountains of Russia. 



Lamellibranchiata. 

 Conocardium trigonale, Conrad. Vanuxemia Tomkinsi, Billings. 



Gasteropoda. 

 Lozonema CoUerana, Billings. Euomphalus de Ceivi, Billings. 



Of the Cephalopoda only one or two undetermined species oc- 

 cur ; whilst the Crustacean representatives are included in the 

 genera Phacops and Dalmannites. 



These fossil species are more or less common to the whole 

 range of Corniferous limestone in the district to which the pre- 

 sent observations are confined. Their specific characters have 

 been minutely examined and described by E. Billings, F.Gr.S., 

 of the Geological Survey of Canada, to whose very elaborate 

 contributions to palaeontology the writer is chiefly indebted for 

 descriptions of such fossil types as come under review in this 

 paper. 



6, Descendinsr the Maitland for three or four miles from the 



