510 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 16, 



be equivalent to the Devonian formation of Europe *. I have been 

 enabled, through the kindness of Mr. S. P. Woodward, to examine 

 the collection of fossils from this district in the British Museum ; 

 and although, from the poverty of organic remains (a circumstance 

 characteristic of the formation also in the United States), the collec- 

 tion is a very small one, there can be no hesitation in assigning the 

 bituminous deposits of the Elk and Mackenzie Rivers to the epoch of 

 the Marcellus shales, and the associated limestones, of the New York 

 Survey. 



The most characteristic fossil of the bituminous beds is a small 

 Pteropodous shell, thickly disseminated through the substance of the 

 shale, apparently the Tentaculites fissurella of Hall, associated with 

 Strophomena mucronata, S. setigera, and Orthis limitaris, of the 

 same author ; at least they cannot be distinguished from his figures 

 of those fossils from the Marcellus shales. 



Two Corals from the associated bituminous limestone are, accord- 

 ing to Mr. Woodward, characteristic of the same epoch, namely a 

 Strombodes (of Hall), having its cysts filled with bitumen, and a 

 Favosites, very like the common F. polymorpha of the Plymouth 

 marbles. From the underlying limestones of the Elk River, Sir John 

 Richardson collected several specimens of Productus (among them 

 P. subacideatus), an Orthis resembling O. resupinata, Terebratula 

 reticularis, a Posidonomya, and a Pleurotomaria. There is a very 

 fine and well-preserved Rhynchonella amongst the collection, remark- 

 able for retaining the original chestnut-coloured bands of the shell. 



Other Formations of the Mackenzie River Basin. — Silurian rocks 

 of Great Slave Lake and River {Onondago Salt G?'oup of Vanuxem 

 and Hall ?) . — After passing through Lake Athabasca, the Elk River 

 is joined by the Unjigah or Peace River, the largest tributary of the 

 Mackenzie, and the united streams, under the name of Slave River, 

 proceed onwards to Slave Lake along the edge of the district of cry- 

 stalline rocks, flowing sometimes through limestone, at other times 

 over granite, and sometimes between the two. The mouths of Slave 

 River open into Slave Lake between the limestone and granite. The 

 limestones along the banks of this stream are, like those of the Elk 

 River, highly bituminous ; but they are chiefly remarkable from their 

 association with extensive beds of compact greyish gypsum, in con- 

 nexion with extremely copious and rich salt-springs. Where they 

 approach the crystalline rocks, they are found, like those of Lake 

 Winipeg, to be highly magnesian, — a circumstance which may deserve 

 attention with reference to the hypothesis of dolomization, which 

 regards the introduction or development of magnesia as subsequent 

 to the deposition of the calcareous matter, and as connected with the 

 proximity of masses containing that earth and heated to a very high 

 temperature. Among the fossils collected from this district which 

 are in the British Museum are Spirifer crispiis, Dalm. 1, Rhyncho- 

 nella 'phoca, Salter, Atrypa Icevis, Vanuxem, Atrypa reticularis, an 



* Bulletin Soc. Geol. Fr. 2 Ser. vol. iv. p. 646. 



