212 The Little Missouri “ Bad Lands.” (April, 
which are scarcely, if at all, distinguishable from the red sand- 
stone of the Connecticut Valley. The metamorphism gradually 
ceases in passing upward, as respects both color and hardness, 
till the influence of the heat wholly disappears. The color of 
these metamorphosed shales thus fades from intense red, or even 
black, through light brick-red to pale red and pale reddish-yellow; 
whilst the texture varies from crumbling scoria and slag, through 
rock of a trappean texture and conchoidal fracture, to finely fis- 
sured baked clay and sandstone, and finally to shales but slightly 
hardened and almost unchanged in color. 
The beds thus altered often present interesting features of 
structure, the indurated clays being extremely fissile, breaking 
up into thin, small, irregularly shaped splinters and fragments, 
which possess a clear, metallic resonance ; the sandstones occa- 
sionally present a prismatic structure, with the planes of cleavage 
oblique to those of stratification, the mass breaking into five or 
six sided prisms, half an inch to an inch or two in diameter, and 
one or two to even two and a half feet in length, almost slender 
enough and long enough for walking-sticks ! 
As already intimated, the beds of lignite vary greatly in thick- 
ness, from a few inches to five or six feet, and even more,! with 
corresponding variations in the amount of metamorphism produced 
by their combustion. In the burning of the heavier of these b 
not only is an immense amount of heat generated, but vapors are 
formed which, in escaping, have also left their interesting records. 
These consist of jagged, chimney-like mounds of breccia that still 
crown many of the buttes and ridges, the softer materials that 
surrounded them having been worn away by denuding agencies, 
leaving them as striking and picturesque features of the land- 
scape. These mounds have sometimes the form of short, thick 
columns, being circular, a foot or two in diameter and a few feet 
high ; at other times they are ten or twelve feet in diameter and 
of about the same height, while they not unfrequently assume 
the form of low, narrow, ragged walls of highly altered rock, the 
material of all these erupted mounds presenting the features of 
a true volcanic breccia. The matter composing these chimneys 
was mostly forced up through small orifices or narrow fissures, 
