Dec, 1912.] Ordovician Section, Lake Huron Area. 45 



but no good exposures have been found. Tctradium bundles 

 occur at 45 feet above the lake, and massive specimens are found 

 4 feet farther up. 



The strata immediately above the Tetradium horizon consist 

 of fissile black shales interbedded with limestone near the base. 

 These strata were formerly regarded as Utica, but they probably 

 represent an older formation than the Utica of New York, and 

 recently Prof. Percy E. Raymond has proposed for them the name 

 Collingwood. Their most characteristic fossil is the trilobite 

 long known as Asaphus canadensis. Triarthriis spinosus, and a 

 graptolite, identified by Dr. Ruedemann as Diplograptiis quadri- 

 mucrouatus, also occur. At Little Current, 11 feet of this Colling- 

 wood shale are exposed, but the total thickness may equal 20 feet. 



7. CiNCINNATIAN BeDS ON MaNITOULIN. 



A. Sheguindah Beds; Eden. 



Along the road from Little Current to Sheguindah, the strata 

 immediately overlying the Collingwood fomiation are exposed at 

 several localities. One of these extends from three miles southeast 

 of Little Current southwards up the hill. Here the top of the- 

 Collingwood is overlaid by shales which near the base are blackisk 

 but much softer. Within 9 feet of the base, these clay shales 

 contain a species of Triarthvus. A small Primitia and a Leptoho- 

 liis extend from the base upward for about 37 feet. The only 

 species of graptolite noted is fairly common, and was determined 

 by Dr. Ruedemann as nearest to Diplogyaptus peosta, but with 

 closer arranged thecae ; it ranges from the base for 43 feet upward. 

 Dalmanella appears at 25, between 37 and 43 feet, and at higher 

 levels. The first trace of limestone was found 43 feet above the 

 base, but limestone layers do not become common until an eleva- 

 tion 100 feet above the base has been reached. 



It is in these upper limestones and in the interbedded clays 

 that the typical Eden fauna listed below occurs. The fossils 

 were examined by Ulrich, Bassler, and Nickles conjointly, the 

 detenninations being only provisional, until microscopic slides 

 can be prepared. Along the Sheguindah road, Amplexopora 

 persimilis, Callopora sigillarioides, Coeloclema communis, Hemi- 

 phragma whitfieldi, Perenopora vera, and a StigmateUa near clavis 

 or nana occur. From the corresponding strata at Tamarac Point, 

 10 miles southwest of Little Current, Aspidopora cf. areolata, 

 Arthropora clevelandi, Bythopora arctipora, and Primitia centralis- 

 occur in addition to those already named. At the corresponding- 

 horizon at Gorrel Point, two miles northeast of Gore Bay, Aspido- 

 pora eccentrica, Bollia per sulcata, Bythocypris cylindrica, Jonesella 

 crepidiformis, Primitia cincinnatiensis, and Acidaspis crossotus 

 are added to the list. At the exposures immediately south of 

 the high Richmond Clay Cliffs, on the eastern side of Cape Smyth, 



