26 C. A. White—Burning of Lignite mm situ. 
forest fires may sometimes have resulted from lightning, it is 
~ not thought probable that a bed of lignite za situ could be 
thus ignited. I believe that in a great majority of the cases 
ignition has taken place spontaneously, like that which is often 
seen in progress in the piles of refuse coal that collect about 
the mouths of coal mines; and yet it is probable that in some 
cases the firing has: been caused by the burning of grass and 
other vegetation upon the adjacent surface, caused by human 
PA ithedate as already stated, beds of lignite are _ burning 
at a few localities, there is evidence that of the m ny thou- 
sands of cases of such burnings that are known ie have oc- 
curred, a large part of them are very ancient, probably more 
ancient than the artificial introduction of fire upon the conti- 
nent. 
The great erosion that the strata of the Laramie Group have: 
everywhere suffered, even in regions where they have been 
fittle. disturbed, has already been referred to.. Upon the up- 
Jands of the region examined by me last summer numerous. 
buttes and knolls occur upon the vary summits of which are 
little patches of the heat-reddened shales, and the slopes of 
which are strewn with the slag of former lignite-fires. These 
are evidently the only remaining traces of beds of lignite that 
once existed at or above the horizon of the tops of these knolls. 
urthermore, on the upland surfaces more or less distant from 
such knolls, one often meets with masses of the well-known 
slag which ‘could have been transported there by no known 
agency, but which have doubtiess settled down from the 
horizon where they were produced by burning sent as the 
surface was afterward lowered by erosion. These examples do 
not occur where erosion has been sont rapid, hoe on the con- 
trary they are where the minimum rate of erosion has occurred. 
Such examples seem to prove conclusively the great an- 
tiquity of — of these lignite-fires, and if, as is supposed, 
these fires took place by spontaneous combustion as La beds. 
of lignite became by erosion daisy ap. ex Oo atmo- 
spheric influence, there is no necessity for considering ihe limit. 
of their antiquity with reference tae uman agency in the pro- 
duction of fire. Indeed, taking this view of the matter there 
appears to be no reason why the earliest of these fires in the 
Laramie lignites may not have occurred as early as, if not 
earlier than, later Tertiary time. 
