318 C. SCHUCHERT MEDINA AND CATARACT FORMATIONS 



Cataract formation. About 106 feet thick. 



Cahots Head member. Upper green shales with very thin magnesian 

 limestones, about 20 feet thick. Helopora fragilis is common in the 

 limestones. At Limehouse this zone is only 6 feet thick. 

 Red, decidedly feri-ughious, shaly limestone, with thin shale zones, 5 

 feet. Helopora fragilis very common here. Other Bryozoa also occur, 

 but not so abundantly as at Limehouse or Dundas. 

 Middle green shales, with occasional thin magnesian limestones, that 

 become more abundant downward; about 40 feet thick. In the 

 shales fossils are scarce, but in the limestones Helopora (two or 

 more species) are exceedingly common. Also here Orthis flahellites 

 and other forms of the Manitoulin member. 

 Manitoulin memher. Greenish magnesian limestones in beds up to 12 

 inches thick, with irregular zones of chert, separated by thin bands 

 of green shale, about 25^ feet. The transition zone to the Whirlpool 

 consists of not over 3 inches of shale. The main horizon for Cataract 

 fossils. At 8 feet above the base, a thin shale abounds in many 

 small fossils, Whitfieldella n. sp.. W. of. oblata, Atrypa rugosa, A. u. sp. 

 Ccelospira planoconvc.ra is common between 8 and 15 feet above the 

 base. 

 Whirlpool memher. Basal heavy-bedded, rippled and decidedly cross 

 bedded, white, or mottled with red spots, or pinkish, fine-grained 

 sandstones, 16.5 feet thick. Much quarried for building stone all 

 along the Credit. At the top occurs Modiolopsis (?) orthonota. 



Disconformity. Base of Siluric. 



Queenston. Top of Ordovicic (Richmondian). Brick-red sandy shales. Ex- 

 posed about 250 feet. 



Collingwood, Ontario, section (4S miles northwest of Cataract). — Five 

 miles to the south of Collingwood rises the high cnesta, "Blue Mountain," 

 the top of which is fully 800 feet ahove Georgian Bay. The section is 

 toward the top of the mountain. 



Lockport dolomite making vertical cliffs at the top of the mountain. Thick- 

 ness present 160 feet (Logan). 



Disconformity. All Rochester and Clinton absent. 



Cataract formation. Thickness about 32 feet. 



Cahots Head shale member covered and replete with springs. Thickness 

 estimated at 20 feet. Loose magnesian limestones along the roadside 

 abound in bryozoans. The top is in all probability eroded away. 

 Manitoulin memher. Thin-bedded, light blue, finely granular, magnesian 

 limestones, without shale partings. At crest of mountain road. 

 Thickness 12 feet, but near Meaford (20 miles to the northwest) 

 attains 29 feet (S. E. Whittaker). Fossils scarce except Leptcena 

 rhomboidalis. 

 Whirlpool member not present here. Last seen at Glen Huron, 12 miles 

 south of Collingwood (Williams). 



Disconformity. Base of Siluric. 



Queenston. Top of Ordovicic. Brick-red sandy shales devoid of fossils, 

 about 45 feet thick. 



