1874.] 261 [Allen. 



Dr. J. P. Kimball, Chief Medical Officer of the Northern Pacific 

 Railroad Expedition of 1873, described to me a locality he visited a 

 few years since near Fort Berthold, where a lignite bed had burned 

 in for a distance of fifty yards and was still on fire. The ground 

 was considerably heated, and the overlying clays baked and red- 

 dened. Lieut. P. H. Ray, Chief Commissary of the same Expedi- 

 tion, informed me of a similar locality on the^Little Missouri, some 

 fifty miles above where we crossed it, which he visited in 1871. He 

 camped on it and found the ground quite warm, although it was late 

 in the season and the weather very cold. 



From other reliable sources I have received additional accounts of 

 beds seen in a state of ignition, and some smokes we saw in July on 

 our right as we crossed the Little Missouri Bad Lands, and supposed 

 at the time to be signal fires of the Sioux, were afterwards attributed 

 to burning beds of lignite. 



The origin or cause of these subterranean fires seems somewhat 

 obscure, but it is evident that they must have arisen from more than 

 a single cause. Several instances are well known of the lignite beds 

 having taken fire from the burning of the prairie grass by the Indians; 

 in some cases these fires lasting for several years. On Heart River 

 the lignite beds exposed in the banks of the stream are said to some- 

 times take fire in this way, and to burn until a rise of the water 

 reaches the exposure and extinguishes the fire. It is also probable, 

 as suggested by Dr. Hines, that the lignite beds contain in themselves 

 the elements of spontaneous ignition, and that in earlier times the 

 fires may have originated in this way. The slopes of the buttes and 

 ridges in which the lignite seams are exposed are usually destitute of 

 vegetation, being in most cases almost vertical, so that it seems in 

 many cases highly improbable that the fires could have reached them 

 from the burning of the adjacent prairies. The theory of Mr. Nicol- 

 let, that these fires may be due [ " are evidently due," he writes ] " to 

 the decomposition, by the percolation of atmospheric waters to them, 

 of beds of pyrites, which, reacting on the combustible materials, such 

 as lignites and other substances of a vegetable nature in their vicin- 

 ity, give rise to a spontaneous combustion " l may not be wholly im- 

 probable. 



It is well known that beds of true coal, when once ignited, will 

 burn for many years, the fires penetrating to a great depth into the 



1 Nicollet's Rep. Hydrogr. Basin Upper Mississippi, p. 40. 



