61 
with the expanded form figured. However, the globular form is too poor 
for identification and the expanded form is very close to R. oweni. A 
number of Strophomenidae with ridged surface markings have been 
described by Holtedahl from the Ordovician of the Kristiania region. 
The form here figured has the same general, peculiarly ridged surface, 
but is believed to be a new species of Strophomena and is consequently 
described as S. ruga. Of the other fossils Dr. Foerste has shown that 
Endoceras is typically Ordovician, whereas the other Cephalopods are not 
distinctive. In this connexion it might also be said that Cyrtodonta is 
much more common in Ordovician rocks than in strata of any other age, 
so that its occurrence in this assemblage is also somewhat significant. 
In conclusion, therefore, it is believed that these fossils indicate an 
Ordovician rather than Silurian age, as has previously been supposed. 
The information is not sufficient to assign them to a definite position 
in the Ordovician, although some facts are worth consideration. 
Halysites gracilis occurs in the Trenton 1 of Manitoba, the nearest 
Ordovician rocks known to those of Great Slave lake, and in the Richmond 2 
of Anticosti. In Manitoba it is found with R. oweni , and in the Anticosti 
faunas 3 Palaeofavosites asper, which is also common on Great Slave lake, 
occurs. At the present time, therefore, the information at hand is 
insufficient to say whether this Great Slave Lake fauna is Trenton or 
Richmond in age. 
Silurian Beds ( Fitzgerald Dolomite) 
The horizon correlated by Cameron 4 with the Fitzgerald dolomite 
contains a fauna that correlates it most closely with the Guelph of south- 
western Ontario. The following fossils were found in a single outcrop 
southwest of Gypsum point. 
Pycnostylus elegans 
Pycnostylus guelphensis 
Spirifer nearest corattiensis 
Phragmoceras sp. 
Poterioceras sp. 
Rizoceras sp. 
Such characteristic fossils as Pycnostylus guelpherms and P. elegans 
occur abundantly in the Guelph of southwestern Ontario and are known 
elsewhere only from beds which according to Williams 6 are transitional 
between the Lockport and the Guelph in southwestern Ontario. The 
Cephalopods have been described by Dr. Foerste in the accoihpanying 
report and his conclusions in regard to age agree with that indicated 
by the Pycnostylus . 
1 Geol. Surv., Canada, Ann. Kept. . vol. XI, pt. F, p. 49 (1899). 
* Contr. Can. Pal., vol. IV, pt. I, p. 69. 
* Geol. Surv., Canada, Mus. Bull. 3, p. 6. 
* Geol. Surv., Canada, Sum. Kept. 1917, pt. C. 
* Williams, M. Y.: Geol. Surv., Canada, Mem. 111. 
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