SILURIC SECTION, ROCHESTER TO LAKE HURON 313 



inches has green weathered shale pebbles of the lower red Queenston, 

 and there is here also much iron pyrite. The under side of the 

 Whirlpool fills into the sun-cracked (the cracks, are sometimes 2.5 

 inches deep), but otherwise almost even surface of the Queenston. 



Disconformity: Base of Siluric. See contact in plate 13, figure 2. 



Queenston brick-red shales barren of organisms. Top of Ordovicic (Rich- 

 mondian). 



Hamilton, Ontario, section (6 miles west of Stony Creek). — -On cuesta 

 back of tke city between the two inclined planes. See Logan, Geology of 

 Canada, 1863, pages 310-334; Spencer, Canadian Naturalist, vol. 10, 

 1883, page 8 ; and Parks, Guide Book No. 4, Twelfth International Geo- 

 logical Congress, 1913, pages 136-139. 



LocTcport dolomite. Present about 37 feet. The base of the formation is best 

 studied at the head of John street beside the road up the "mountain." 

 At the very base here occurs an iron-pyrite fine-grained sandstone 

 up to 3 inches thick. This is followed by a dolomite 2 to 4 inches 

 thick, slightly sandy, pyritiferous, and with shale pebbles up to 1 

 inch in diameter, derived from the Rochester below. Higher there 

 usually occurs a thin irregular shale (in layers or pockets up to 4 

 inches thick) of reworked Rochester, indicating that this formation 

 had not yet been covered everywhere. Over these overlapping basal 

 deposits follows the regulation thin-bedded, cavernous, dark Lockport 

 dolomite, but here devoid of chert nodules through a thickness of 5 

 feet. In the next higher 18 inches there are some of these diagenetic 

 nodules, followed by light gray, thin-bedded, fine-grained dolomite that 

 becomes more and more replete with nodules (many containing Asty- 

 lospongia proem or sa and Anlocopma granti) and chert stringers. (For 

 a more complete f auual list see Parks, 1913 : 137. ) The great majority 

 of the graptolites (Dictyonemoid) described by Bassler are from these 

 chert beds. 



Disconformity. Contact sharp between adjacent beds. The break in sedi- 

 mentation is here clearly made out, as the greater part of the 

 Rochester is absent. 



Rochester formation. Thickness about 15 feet. 



The greater part of the upper Rochester is absent. 



A series of dark green, somewhat calcareous, limy shales, interbedded 

 with thin bands of fine-grained magnesian limestones (the "blue build- 

 ing stone"). Fossils are practically absent in the upper 6 feet, 

 followed by a zone a few inches thick replete with Trepostomata 

 Bryozoa, more rarely Fenestella, Dictyonema, Meristina, and Rhyn- 

 chotreta americana. The most abundant fossils throughout this zone 

 are crinoidal ossicles, and none of the Rochester guide fossils are 

 present. 

 The contact with the Clinton is sharp, but the fauna indicates no time 

 break. At the very base of the Rochester there is a shale zone 1 

 inch thick, followed by a Clinton-like limestone 2 inches thick, with 

 Atrypa reticularis. Another shale zone, several inches thick, follows, 

 and is succeeded by a thin bed of magnesian limestone more like 



