SILURIC SECTIONS, ROCHESTEK TO LAKE HURON 319 



Richmondian. Green sandy shales with thin zones of magnesian limestones 

 having minute Bryozoa, Ostracocla, Zy<jospira recurvirostris and Le- 

 perditia Qf..C(Ecigcna. Thickness about 90 feet. 

 A thick series of light blue, somewhat calcareous shales. At the top thin 

 zones of limestone occur rarely, but increase in quantity more and 

 more downward, and in the same way occurs a greater abundance 

 of characteristic Richmondian fossils. From the dominantly cal- 

 careous strata m.the lower part of the section, with many fossils, 

 one rises higher into more and more.shaly and then sandy strata, the 

 corals and brachiopods drop put, the bryozoans continue,, but the 

 : . : Trepostomata finally also (Jrop put,, leaving only the minute forms 

 to attain the top of the green shales. Thickness up to Queenston 

 not clearly made out, but apparently not less than 340 feet. Some 

 of the Richmondian fossils are Tetradium fibratum {TSLve) , Strepte- 

 lasma rusticum (rare), Hebertella insculpta (common), Amdonychia 

 radiata, Modiolopsis concentrica, and Whiteavesia pholadiformis. 



Owen Sound, Ontario, section (38 miles west of ColHngiuood). 



Lockport limestone well exposed in West Owen Sound. Heavy-bedded, fine- 

 grained, light gray, fossiliferous dolomite, at least 70 feet thick. 

 "White rock" of quarry men. 



Disconformity. Actual contact not seen. 



Cataract formation. About 130 feet (thickness determined by Williams). 

 CaJ)ots Head member. Covered zone of shale, with red zones and fer- 

 ruginous bands. Thickness estimated at 50 feet. 

 Blue-green shales with thin-bedded, nodular, and even-bedded limestones 

 replete with Cataract fossils. Thickness 25 feet. Seen at Wright's 

 flour mill in West Owen Sound. 

 Manitoulin limestone member, 30 feet thick. Thin-bedded, light blue 

 ("blue rock" of quarrymen) to gray, finely granular, magnesian lime- 

 stones, with thin zones of chert. Quarried for lime to the east of 

 Owen Sound. In the upper 10 feet the chert zones abound in fine 

 fossils, among them Rhinopora verrucosa, Platystrophia biforata, 

 Orthis flabellites, Dalmanella elegantula, Schuchertella subplana, Lep- 

 tcena rhomboidalis, and Coelospira planoconvexa (exceedingly com- 

 mon here). 



Disconformity. Base of Siluric. 



Queenston formation. Top of Ordovicic (Riclnnondian). Brick-red, soft, 

 sandy shales, with very thin sandstones in the upper 8 feet; about 

 50 feet. No fossils. In places near the top occur zones of sun- 

 cracking with the prisnis small. Thirty feet beneath the top occur 

 lumps of secondary impure gjTpsum. Forty feet from- the Cataract 

 in a thin green shale occur Bebertella sinuata, Richmondian Bryozoa. 

 Leperditia ct.vwcigena, an& other O^trncodsi. '^ 



■■ Calots Head^' Bruce PSnihsula; Ontario/ s&cti^ (-58 miles northwest 

 'of Owen Sound) .-— Inf oiroal^on; |rom , T)x. %: " Y;- 'WHtiains;""^ Also see 

 Logan, Geology of Canada, 18G^,ljiages '319-320. 



Lockport dolomite. Massive cliff-making. Present 165 feet (Logan). 



