142 Scientific Intelligence. 
um left in coal grates from the combustion of ordinary mineral 
coal, 
The region of the Bad Lands, on the Little Missouri, is one of the 
fire to the action of decomposing pyrites on lignites and other 
material of a combustible nature 
_ metamorphism The baked rocks, besides giving their red tints 
to the co or greatly retard the erosion of the buttes 
ridges consisting of them. Over areas of thousands of square 
miles t us in a sure determine the surface contours 
and protect the hills from rapid denudation. Fragments of pum- 
ice have been found on the Missouri as far south as Port Pierre, 
and the early explorers supposed them to be the products of un- 
