1855.] ISBISTER — NORTH AMERICA, ETC. 511 



Orthis, two small Spirifers, like S. trapezoidalis, Dalm. and S. pisum. 

 Sow., and fragments of an Encrinital stem like that of Actinocrinus. 

 Sir George Back, on his expedition down the Great Fish River, col- 

 lected some fragments of Corals along the south shore of Slave Lake, 

 which were considered by Mr. Stokes and by Mr. Lonsdale to belong 

 some to Catenipora escharoides, and one to the genus Sti^omatopora 

 of Goldfuss, and probably to his species *S. polymorpha. From the 

 circumstance of these fossils being chiefly Upper Silurian, it has been 

 conjectured, with every appearance of probability, that the salt-springs 

 may belong to the " Onondago Salt Group " of the " Helderberg 

 division" of the New York system. 



Carboniferous Series {]\Iountai7i Limestone^). — Some of the 

 organic remains procured by Sir John Richardson on a previous 

 expedition from other points along the Mackenzie River would appear 

 to indicate an ascending order in some of the deposits of that district 

 from the Devonian limestones and the shales containing Tentacidites 

 into beds of Carboniferous, or perhaps more recent age. In some 

 specimens from the limestone* of the " Ramparts " in the lower part 

 of Mackenzie River, brought to England in 1826, Mr. Sowerby dis- 

 covered Terebratula sphcBroidalis, together with a species common 

 in the carboniferous limestone of Nehou in Normandy, some Froducti^ 

 and a Coral of the genus Amplexus. From other parts along the banks 

 of the same river several Terehratulce were procured, one resembling 

 T. resupinata, one Spirifer acutus, a Cirrus, some Crinoidal remains, 

 and Corals, — a somewhat perplexing assemblage, if they were all 

 collected from the same spot. Most probably some of the specimens 

 had been derived from the boulders and transported fragments with 

 which this part of the country is covered. 



Lignite Formation. — The difficulty of deciding upon the age of 

 the beds through which the lower part of Mackenzie River flows, is 

 increased by the occurrence among them of a Lignite-formation, 

 covered in parts by deep beds of sand, capped by boulders and gravel. 

 The soft friable shales forming the bank of the river near its termi- 

 nation in the Arctic Sea are also strongly impregnated with alum. 

 These aluminous shales cover a large portion of the delta of Mackenzie 

 River, are continued along the banks of Peel's River to the foot of 

 the Rocky Mountains, and have been traced for a considerable 

 distance along the coast, and also along the shores of Great Bear 

 Lake. The aluminous shale is constantly associated with the bitu- 

 minous formation, into which it often passes. 



The lignite-formation is still more extensively developed ; and, as 

 the occurrence of coal in any form in these high latitudes is a 



* The limestone of the " Ramparts," which appears again lower down at a spot 

 called the "Narrows," is continued in a westerly direction to the Rocky Mountains, 

 the lower elevations of which are composed of it in that portion of the range through 

 which Peel's River takes its course. It has all the characters of the Mountain 

 Limestone of English geologists, — a formation extensively developed in Russian 

 America, where, as will be subsequently noticed, it has been clearly identified by 

 its organic remains. 



