
COMBUSTION OF LIGNITE BEDS. .. 165 
edge of the Lignite Tertiary, and were also found in almost all the locali- 
ties in which lignite occurred. The products of the combustion were first 
noticed as fragments of rock indistinguishable in appearance from modern 
lavas, and scorias, strewing certain banks, and in the beds of streams. 
The connection between these traces, and the combustion of the lignites 
was, however, soon established, and beds actually found which had been 
burned but a short way in from the outcrop. The bank of the Souris 
River,—as stated in the Preliminary Report already referred to—in one 
place shows an amphitheatrical depression a few feet below the general 
prairie level, in front of which a great quantity of lignite clinker, often in 
large masses, was strewn down the slope toward the river. <A bed of lig- 
nite six feet thick, elsewhere well exposed and overlaid by about five feet 
of clay and drift, was here completely burned away, (Plate IV., Fig. 1.) 
By reference to the detailed accounts of the various localities, many 
similar instances will be found. 
387. The effects produced on the lignites and associated beds, as 
derived from the examination of numerous widely separated localities, 
admit of classification and general statement. The lignites themselves 
appear to be invariably consumed in their entire thickness, and their 
immediate horizon is represented by a layer of ashy clinker, or of a 
material resembling scoriaceous lava, and vesicular in structure. The 
fused masses are always dark coloured, generally blackish or dark grey, 
but sometimes opaque bluish or brownish-black. This clinker bed is 
doubtless composed of the ash of the lignite itself, and any intercalated 
shaly layers, or portions of carbonaceous clays associated with it; the par- 
ticles of which have been brought more intimately in contact with the 
burning material. The fusion may also be aided by the alkalies and alka- 
line earths of the lignite ash, which differs in composition from the 
surrounding clays. 
388. The alteration extends much further above the position of the 
lignite bed than below it. The surrounding layers are very generally 
of the nature of fire-clays, and contain little or no iron, and a smal 
proportion of undecomposed felspar, or other fusible mineral, and are 
consequently very refractory. Those immediately above the lignite, are 
frequently altered to hard jaspery, or porcelain-like rock, breaking with 
sharp conchoidal fracture, sub-translucent, and of greyish-blue and 
dull greenish tints. In this substance, impressions of the stems and 
leaves of plants are, however, sometimes recognisable The porce- 
lainized beds are generally traversed in all directions by rusty fissures, 

