210 The Little Missouri “* Bad Lands.” [ April, 
and from an unusual source, has also acted here on a grand scale, 
but as a preserving rather than as a destroying agent. Beds of 
lignite, a few inches to several feet in thickness, occur interstrat- 
ified with the deposits of sand and clay. The deep, sharp gullies 
formed by the action of water have exposed these beds of lignite 
for long distances. This exposure to atmospheric influences 
seems to have in some way produced spontaneous combustion of 
the lignite, for there is abundant evidence that some of the igneous 
action about to be described occurred before the close of the 
terrace epoch. Whatever may have caused the coal beds to take 
fire, the fact remains that for long ages their destruction has 
been going on, and even still continues, producing geological re- 
sults of a most interesting and important character. When once 
well ignited they seem to burn for long periods, the fires pene- 
trating far into the interior of the hills, extending at times till 
all the coal seams over very large areas are consumed, At the 
present time these fires are known to sometimes originate from 
the prairie fires, which occasionally sweep over these lignite ex- 
posures and ignite the coal. But a large proportion of the beds 
that have been destroyed appear to have been so situated that 
prairie fires could not have reached them, the exposures being 
about midway up the bare, nearly vertical faces of very hi 
bluffs. Wherever the lignite beds have been burned, their 
former position can be easily detected by the bright red bands of 
the hardened overlying clays and sands which have been meta 
morphosed by their combustion, these red bands being often 
traceable by their color for long distances, occurring at the same 
level in butte after butte. 
The burning of such large masses of lignite must of course, €s- 
pecially when the beds have considerable thickness, produce an 
intense heat ; yet the metamorphism here seen seems sometimes 
to be on too grand a scale to be the result of so limited a cause 
The thickness of the strata more or less changed in texture and 
color by the heat varies, of course, with the thickness of the seam 
of lignite the burning of which was the source of the metamor- 
phic action, and hence ranges from a few feet to twenty or thirty, 
and occasionally to upwards of fifty! In many cases the heat 
was sufficient to partly or wholly fuse the shales immediately in 
contact with the burning lignite, giving them a semi-vitreous 0 
porcelaneous texture. At the bottom of the series of metamor- 
phosed beds we have usually a layer of cinders and clinker, 
which occupies the position of the former lignite bed itself. The 
SEN SI ort 
E SBAA E G Aa Pe 
