LOWER SASKATCHEWAN RIVER VALLEY. 
9 
* 
The thin-bedded dolomites of the next higher division (g) 
contain very few fossils at most levels. Certain strata, however, 
hold an abundance of the shells of a small lamellibranch and the 
ostracodes indicated in the following list: 
Pterinea occidentalis Whiteaves. 
Phanerotrema cf , ocridens (Hall). 
Gomphoceras sp. 
Gomphoceras parvulum Whiteaves. 
Isochilina grandis var. latimarginata Jones. 
Leperditia hisingeri Jones. 
Leperditia hisingeri var. egena Jones. 
Leperditia hisingeri var. caeca Jones. 
In the higher beds of the section, fossils which are deter- 
minable are scarce. One or more species of Stromatopora and 
Favosites are met with. The type material of the coral Petraia 
( Pygmaea ? var) occidentalis Whiteaves and Lyellia affinis Bil- 
lings, appear to have been derived from these upper beds. 
Tyrrell 1 also records from them Stropheodonta acanihoptera . 
Close comparison between the faunas of the Grand Rapids 
section and those of eastern Silurian sections owing to dearth 
of common species is difficult. The dominance in the lowest 
fauna of the section of such a genus as Conchidium , however, 
makes it probable that the base of this section represents a 
Silurian horizon not earlier than Clinton and probably of early 
Niagara age. It appears to represent a portion of the Stonewall 
limestone 2 of south central Manitoba. 
Above Grand rapids the river flows for a short distance 
between cut banks of boulder clay which are 60 feet high in 
places. About t\ miles above the end of the Grand Rapids 
tramway the dolomites are again exposed in flat-lying beds at 
Roche Rouge rapids. These exposures, together with others at 
a third rapid just below Cross lake, represent the higher beds 
of Grand Rapids section. On the west side of Cross lake, ledges 
of dolomite 4 to 6 feet high are exposed on Burnt island and on 
* Ibid. 
* Geol. Surv., Can., Sum. Rept. 1912, p. 248. 
