460 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



a layer of fiat clay pebbles, covered by a highly polished coating of iron 

 oxide, suggests aridity and warmth, with the production of a desert var- 

 nish. That all of these deposits were forming on dry land is shown not 

 only by their character, but also by their contact with the underlying 

 rock. The sketches (figures 6 and 7, page 444) taken from my note- 

 books show this contact near Iron Eidge, Wisconsin. The basal bed of 

 the succeeding dolomite contains limestone pebbles and fragments of 

 Stromatoporoids. 



In northwestern Ontario the basal Siluric beds are marine limestones 

 and dolomites resting, probably with a disconformity, on red Queenston 

 shales. From their nearly continuous exposure along the lake front in 

 the township of Keppel, from Owen Sound to Cape Commodore, the 

 name Keppel dolomites will be applied to them. At Cape Commodore 

 109 feet of Queenston shales rest on the Hudson, and are followed by 

 about 36 feet of thin-bedded Keppel dolomites. Then follow about 150 

 feet of red shales and some sandstones. These red beds are again well 

 exposed at Cabots Head, the northeastern point of the great peninsula 

 separating Lake Huron and Georgian Bay. Here they are 103 feet thick, 

 and consist of red, marly sandstones, partially striped and spotted with 

 green, and interstratified with beds of red and green argillaceous shale, 

 none of them, however, exceeding 6 or 8 inches in thickness. This is the 

 Tobacco-pipe rock of the Indians, and it is succeeded by 55 feet of green, 

 calcareo-argillaceous shales and thin-bedded limestones, above which fol- 

 lows the Pentamerus limestone, considered the western extension of the 

 Walcot of Niagara. The red and green beds will be named the Cabots 

 Head beds, and they are believed to be the westward extension of the true 

 Medina sedimentation, which at Niagara is about 125 feet thick. 65 The 

 Keppel dolomite is an earlier marine deposit before the sands and muds 

 from the Appalachians reached this point, or during the earlier period of 

 the erosion of the folded red beds of the Ordovicic. Fragments of the 

 Cabots Head beds contain Helopora fragilis and Phwnopora explanata 

 Hall, the former abundant in the Upper Medina of the Niagara section, 

 and occurring also with the Phaenopora in the Clinton ore bed at Flam- 

 boro Head. Eastward from near Collingwood and Nottawassaga the red 

 Medina beds are separated from the overlying Clinton by the gray band, 

 which from its exposure at Thorold, Ontario, on the Welland Canal, will 

 be called the Thorold quartzite. This band is traceable eastward, occur- 

 ring everywhere at the top of the Medina from this point to Eochester 



65 The entire series has recently been named the Cataract formation by Schuchert. 

 Preliminary announcement of papers Geol. Soc. Am., New Haven Meeting, Dec, 1912. 



