147 



From the evidence thus at hand it would seem that so far as the eastern lisrnite area is 

 concerned the metamorphosis has been determined entirely by the combustion of lignite, and 

 no doubt the same explanation holds true to some extent of those in British Columbia, although 

 to this there has been added the effect of volcanic action. 



In endeavouring to account for the fires which produced these results Alleni considers 

 that more than one cause may have been operative, and he recalls well known instances 

 of beds which had been ignited by the burning of prairie grass by Indians, in some cases 

 the fires lasting for several years, in others until they were extinguished by the rising river. 

 Dawspn2 similarly refers to the fires of Indians or traders' camps, as well as to prairie fires 

 as the known cause in some instances. With respect to the latter, he points out that even 

 when burning over very scantily grassed areas there is sufficient heat to ignite the bois de 

 vaches, or dried Buffalo excremeni, with which the surface is strewn— a much less combusti- 

 ble fuel; and he considers this a wholly satisfactory explanation. 



Allen, on the other hand, attaches importance to the theory of spontaneous combustion 

 originally suggested by Nicollet^, supposed to be due to the percolation of atmospheric waters 

 upon beds of pyrite which in their decomposition generated sufficient heat to fire the lignite. 

 In opposition to this view Dawson points out that this is not properly spontaneous combus- 

 tion, and that while the ignition of bituminous beds is well known to be due to the oxidation 

 of pyrites, this can hardly be applied to the lignite beds, which a chemical analysis shows to 

 be almost entirely devoid of that mineral. Dawson has also cited instances of lignite beds 

 burned at the outcrop only^, a fact which may be interpreted to mean that the fire had been 

 extinguished before making great headway, or that the absence of oxygen in the interior of 

 the beds had prevented its extension in that direction. But Allen, on the other hand, shows 

 conclusivelyS that the fire very generally extended throughout the entire bed and generated 

 large quantities of explosive gases which developed great pressure. This is evident from the 

 occurrence of numerous volcanic chimneys which reproduce in miniature all the features of 

 active volcanoes, but have their origin in the lignite beds. 



There is a "manifest want of agreement in the interpretation of all the observed facts. It 

 is quite clear that the lignite does burn independently of fresh supplies of oxygen, and that 

 it must be capable of ignition otherwise than through the agency of man or prairie fires. It 

 is equally clear that there is not sufficient pyrite present to cause such a conflagration by its 

 oxidation. Some other cause must be sought. 



Allen expresses the opinion that the peculiar metamorphosis exhibited by the lignite 

 beds has extended back to a very remote period^, and that its beginning must have been 

 anterior to the close of the drift period, (Op. cit), and prior to the terrace epoch. His reason 

 for this opinion is based upon the fact that igneous material in a water-worn state occurs in 

 the drift which covers the general surface of the country, often many miles from the nearest 

 seat of metamorphic action, as well as in the terraces that border the larger streams. 



1 Proc. Bost. Soc. Nat. Hist., 261. 



2 Brit. N.A. Bound. Conim. 



3 Rep. Hydrogr. Basin Upper Missouri, p. 140. 



4 Brit. N.A. Bound- Comm., p. 165, pi. IV, f. 1. 



5 Proc. Bost. Soc. Nat. Hist., p. 249. 



6 Proc. Bost. Soc. Nat. Hist. 



