320 C. SCHUCHERT MEDINA AND CATARACT FORMATIONS 



IHsconformity. 



Cataract formation. Thickness 60 feet. 



Cahots Head meml)er. Top probably eroded away. Soft gray shale 

 locally tinged with red, 4 feet. 

 Thin-bedded limestones with branching Favosites and Helopora fragilis, 



5 feet 

 Hard green argillaceous shale, 36 feet. 

 Manitoulin memher. Massive dolomite, 15 feet. 

 Disconformity. Base of Siluric. This contact is illustrated in plate 14, figure 2. 

 Queenston. Top of Ordovicic (Richmondian). Hard and soft red shales, 

 about 45 feet, down to level of Lake Huron. The last place to the 

 north that these red shales are seen, for on the Manitoulins all of 

 the strata beneath the Cataract are calcareous normal marine deposits 

 and have an abundance of Richmondian fossils. 



Manitowaning , Manitoulin Island, Ontario, section (JfO miles north- 

 west of Cahots Head). — Seen by the writer in 1912 under the guidance 

 of M. Y. Williams. See Williams, Guide Book Xo. o, Twelfth Interna- 

 tional Geological Congress, 191e3, pages 89-97. 



Lockport dolomite. Actual thickness as measured by Williams 240 feet 

 (Bell's 450 feet was calculated from the dip). 



Disconformity. 



Cataract formation. (Clinton of Bell.) Thickness averaging 100 feet. 



Cahots Head memher. Usually a covered zone of friable red clay (red 

 marl of Bell), almost barren of fossils, from 27 to 66 feet' thick. 

 At the top the shales are nearly always oxidized into green shale by 

 percolating waters. 

 Manitoulin memher, 50 to 60 feet thick. Thin-bedded, gray to yellowish, 

 fine-grained, magnesian limestones to massive dolomites, without 

 shale partings. In the upper 20 feet there are many small reefs 

 of Bryozoa, Stromatopora, and corals. Fossils as pseudomorphs. 

 Clathrodi^tyon vesiculosum, Holy sites microporus, Heliolites, Fa- 

 vosites venustus. Diphyphyllum vennorl. AcervuUria (?) gracilis, 

 Pachydictya crassa. Platystrophia hiforata, Orthis ffahellites, Heher- 

 tella cf. daytonensis. DalmanrUn clegautula, Rhipidomella hyhrida, 

 SchucherteUa suhplana. Camurotwchui neglecta, Atrypa n. sp., Ccelo- 

 spira planoconvexa, Whit field ella, Cyclonema rancellatum, etc. 



Disconformity. Queenston red shales absent and transformed into the 



Richmondian formation. The best exposures are at Clay cliff on the eastern 

 end of the island, where good fossils are plentiful in a Richmondian 

 section at least 160 feet thick. Beneath are about 100 feet of 

 Lorraine, and 130 feet of Eden. Deep wells give the thickness of 

 the entire Cincinnatian deposits as not less than 435 feet. 

 East of Manitowaning 1.5 miles may be seen along the roadside a good 

 exposure of the uppermost Richmondian in contact with the Cataract 

 sandy limestone. Below these Siluric beds are 12 feet of greenish, 

 clays without fossils, followed by a series of thin-bedded, sandy and 

 shaly, magnesian limestones, 15 feet thick, with many Bryozoa through- 

 out, other fossils being alrnost absent. 



