SILURIC SECTION, ROCHESTER TO LAKE HURON 311 



Rochester shale. Thickness about 39 feet. 



Dark blue shale beds that become more and more fossiliferous and softer 

 downward. The greatest abundance of fossils is in the lower 15 

 feet, in which may be noted Caryocrinus ornatus, 8tephanocrinus 

 angulatus, Ichthyocrinus Icevis, Eucalyptocrinus ccelatus, Orthis flahel- 

 Utes, Spirifer niagarensis, Dalmanites limulurus, Lichas holtoni, many 

 Bryozoa, etc. (See Parks, pages 131-133, for more complete fauna.) 



Clinton limestone. Thickness 14 feet. 



Irondequoit limestone in one bed 4 feet thick. Hard, crystalline, pinkish, 

 crinoidal limestone, with zones of stylolites. There is no break be- 

 tween this bed and the Rochester, as the fauna continues largely 

 from one to the other. 

 Wolcott limestone memher. Thin-bedded magnesian limestones, with 

 green shale partings, 10 feet thick. At 18 inches above the base 

 Pentamerus oMongus is common and more rarely StricJclandinia 

 canadensis and Dinoholus conradi. 

 The base of the Clinton is somewhat irregular in form and pyritiferous. 

 One inch of shale separates it from the Medina. 



Disconformity. Contact sharp between adjacent beds. 



Medina formation. Thickness about 25 feet. 



Dcedalus archimedes bed at the top 18 inches thick. Locally the entire 

 bed is made up of these lamellar and spiral burrows. On the under 

 side of this bed occurs Arthrophycus alleghaniense. In other places 

 are seen regularly bedded gray sandstones ("gray band") with thin 

 green shale partings through a thickness of 6 feet. This is the chief 

 horizon of A. alleglmnicnse. Then a red sandy shale zone, barren of 

 fossils, for 3 to 4 feet, below which are about 15 feet of thick -bedded, 

 somewhat cross-bedded, gray and red mottled sandstones. 



Cataract formation. Thickness about 80 feet. Not well exposed. For fauna 

 see Parks, pages 135-136. 

 The Whirlpool heavy-bedded basal sandstone is here 6 feet thick. The 

 basal 4 inches has much pyrite and green shale pebbles derived from 

 the Queenston. The sandstone also fills sun-cracks in the red shales 

 below. 



Disconformity. Base of Siluric. 



Queenston brick-red shales, exposed for over 100 feet. Top of Ordovicic 

 (Richmondian). 



Stony Creelc] Ontario, section (10 miles west of Grimshy). — On cuesta 

 in gnlch directly back of village. The Canadian Pacific Eailway crosses 

 oveT the month of the gulch. This is the finest single exposure along the 

 entire cuesta in Ontario, but above the Cataract is difficult of access. 



Lookport dolomite. Present about 32 feet. 



At the top are seen thin-bedded, chert-bearing, gray dolomites with a thick- 

 ness of about 12 feet. Below this are about 20 feet more of gray 

 dolomites with far fewer chert nodules. The base of the Lockport 

 is decidedly sandy and pyritiferous and the weathering away of this 

 zone easily distinguishes the contact with the Rochester. 



