310 C. SCHUCHERT MEDINA AND CATARACT FORMATIONS 



Thorold, Ontario, section (10 miles west of Niagara Gorge). — Eecon- 

 structed from Logan, Geology of Canada, 1863, pages 313, 322-323. 



Lockport dolomite. Present about 83 feet. 

 Eroded unconformity as at Niagara Gorge. 

 Rochester shale. Thickness about 71 feet. 



Dark bluish bituminous limestone, often rich in Rochester fossils. Thick- 

 ness 8 feet. Many corals, Stephanocrinus angulatus, Eucalyptocrinut 

 decerns, Garyocrinus ornatus, etc. 

 Bluish gray cement rock. Thickness 8 feet. 



Bluish black shales, with thin bands of impure limestone having Dal- 

 manites Umulurus. Thickness 55 feet. 

 Clinton formation. Thickness 26 feet. 



Irondequoit limestone member. Gray, coarse-grained, subcrystalline lime- 

 stone, with iron and copper pyrites. Thickness 10 feet. Rhyncho- 

 treta cuneata, Whitfieldella cylindrica. 

 Wolcott limestone memher. Bluish gray magnesian limestones with shale 

 partings. Thickness 10 feet. Common near base, Pentamerus o6- 

 longus and StricMandinia canadensis. According to Logan these 

 two members thicken to the west. 

 Bluish drab argillaceous limestone, a cement rock. Thickness 3 feet. 

 Bluish gray limestone with much iron pyrite. Thickness nearly 3 feet. 

 Disconformity. 

 Medina formation. Thickness exposed 14 feet. 



Bluish green argillaceous shale, with ArtUrophycus alleghaniense. Thick- 

 ness 4 feet. 

 Thorold member or "gray band." A white fine-grained sandstone. Thick- 

 ness 10 feet. 



Grims'by, Ontario, section (20 miles tvest of Thorold). — In cuesta along 

 both sides of Forty Mile Creek, back of the ^'Village Inn" (see Parks, 

 Guide Book No. 4, Twelfth International Geological Congress, 1913, 

 pages 130-136). 



Lockport dolomite. Present 12 to 25 feet. 



Gasport limestone member. A thick-bedded crinoidal limestone with a 

 fauna that is essentially Rochester in character (Atrypa nodostriata, 

 Rhynchotreta americana, Spirifer crispus, 8. radiatus, Whitfieldella 

 nitida, many Bryozoa, etc.), but it also has Spirifer eudora and 

 Eucalyptocrinus tuberculatus. 

 DeCew member. The basal thin-bedded, impure, undulatory limestone 

 (cement rock) has a thickness of 8 feet. At the head of the falls 

 and in the cliffs above, the contacts with the Rochester and the Lock- 

 port are well shown. The upper contact is seen to have decided 

 undulations with the pyritiferous layer at the base of the Gasport 

 limestone. The higher beds are harder than those of the DeCew, and 

 therefore make projecting cliffs. 



Disconformity. Contact between adjacent beds easily found, but the lithic 

 difference not marked. Time break short, with about 20 feet of the 

 Rochester lost through erosion. 



