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splinters are fusible on the edges, before the blow-pipe, with greater 
or less difficulty. In their fusibility they range from 4:5 to 6 of Van 
Kobell’s scale, and when fused they form translucent beads. The thick- 
ness of the beds thus greatly altered is generally not more than a few 
inches. In the Bad Lands section a very fine white clay, containing 
numerous impressions: of plants, rests immediately on a lignite, which 
at a short distance, was found to be completely consumed, the repre- 
sentative of the white clay, being apparently a hard porcelain-like 
material of this kind, of pale bluish-grey colour, and waxy lustre. — | 
389. Other clays and clay-shales not so closely in contact with the 
lignites, are generally hardened into whiteish and cream-coloured rocks, 
resembling tiles or biscuit porcelain; and in these the impression of plants 
are often preserved with great beauty. I was not, however, so fortunate 
as to find any locality in which large collections of plants in this fayour- 
able state of preservation could be obtained. The clays, or shaly-clays, 
seldom hold enough iron to give them a red hue when metamorphosed. 
The} sandstones and coarser arenaceous clays, are not usually much 
indurated or otherwise altered, except in colour; but generally con- 
tain sufficient iron to cause a moderately striking red colouration, 
and some beds are very deeply tinted. Such sandstones are among 
the most prominent marks of the combustion, and were observed in a 
great number of localities. In the Bad Land region, several isolated 
buttes capped with intensely red sandstone, which had a remarkable 
prismatic structure, were seen. The structure resembled, on a small | 
scale, the columnar appearance of basalt, the sandstone being divided by 
joints into vertical prisms, and breaking along these nearly at right-angles 
to its original bedding. The rock here precisely resembles ordinary red 
brick, and gives out a faint-ringing sound when struck. Such localities, 
Mr. Allen, who has studied similar metamorphism in Dakota and Mon- 
tana, believes to indicate former vents by which the pent-up gases arising 
from the fire have found exit. (Plate VIL., Fig. 1.) 
390. The effect of the combustion of the lignites over large regions, 
though to indurate the surrounding beds, is evidently from its observed 
relations with great denudation, more destructive than conservative. The 
strata appear to be cracked and fisswred in such a way by the action, as 
to allow the entrance of surface waters to their mass, and accelerate their 
removal, 


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