THE ORDOVICIAN ROCKS OF LAKE TIMISKAMING. 
5 
bedded, buff to light grey dolomites, 10 to 15 feet thick, form 
the highest point on. the hill. No fossils were found in these 
beds. 
The Pentamerus oblongus- A try pa reticularis beds are prob- 
ably to be correlated with the Pentamerus beds 8 to 10 feet 
above the base of the Niagara (Lockport) dolomite of Mani- 
toulin island and the Bruce peninsula, and thus indicate the ap- 
proximate base of the Niagara. 
The same horizon also occurs on Farr island about the mid- 
dle of a 12-foot section of thin-bedded blue grey limestone where 
the following fossils were found: Favosites niagarensis Hall, 
Syringopora retiformis Billings, Haly sites catenulatus Linnaeus, 
Pentamerus oblongus Sowerby, Gypidula sp. and Rhynchotreta 
cuneata americana Hall ?. On the west side of Mann or Burnt 
island the following fossils were found, loose, on the shore: 
stromatoporoids, Zaphrentis stokesi E. and H., Favosites niagarensis 
Hall, Halysites catenulatus Linnaeus, Pentamerus oblongus Sower- 
by, Rhynchotreta cuneata americana Hall ?, Camarotoechia 
obtusiplicata (Hall) ?, Whitfieldetta sp., Orthoceras sp. 
Near the northwestern extremity of the island the follow- 
ing section occurs: 8 feet above the lake (low water) about 
3 feet of thin-bedded chocolate-brown dolomite protruding 
through the shingle of the beach; beginning 16 feet above the 
lake, 10 feet of green even-bedded shale, mud-cracked near the 
base ; on top 6 feet or more of rather thin-bedded dolomites . 
containing the following fossils: Streptelasma sp., Strophonella 
sp., Orthis fiabellites Foerste, Pentamerus oblongus Sowerby, 
Atrypa reticularis (Linnaeus), Pleurolomaria sp. 
Chief island is a glaciated knob of Huronian quartzite cut 
by diabase dykes. The irregularities of its sloping sides contain, 
at a few places (Plate I A), conglomerates composed of sub- 
angular Huronian pebbles enclosed in a limestone or dolomite 
matrix (Plate I B). On the south side of the island, a lenticular 
area of dolomite about 100 feet in diameter dips downward to the 
lake. It appears to have a maximum thickness of about 5 feet. 
From this point, Barlow obtained some lower Niagara fossils. The 
dolomite contains throughout small pebbles of Huronian rocks. 
