24 C. A. White—Burning of Lignite in situ. 
time of the trotting horse will be reduced to within one second 
of the limiting value. 
It will be understood of course that it is not claimed that 
the numerical values here determined are at all precise. In 
all probability the true value, L, is somewhat larger than 92 
seconds, and may possibly be as great as 100. This value can 
probably be determined with considerable accuracy in the 
course of ten years. It is, however, quite clear that the limit- 
ing speeds of trotting and of running horses, can differ at most 
by only a very few seconds. 
Art. UL—The Burning of Lignite in situ; by CHARLES A. 
WHITE. 
[Published in advance by permission il the Director of the U. S. Geological 
Survey. ] 
mapa ae those portions of Colorado, Wyoming, Mon- 
and ota which are occupied by the Laramie Group, 
one aprsis nfreas: that portions of its strata which are ex- 
posed in the eae and buttes have a conspicuous brick-red 
color. Upon close examination of at least a large part of these 
reddened strata it is evident that they originally bore the buff, 
aude or yellowish colors of their associated strata, and that 
they have received their present red color from the same source 
that bricks do, namely, from heat. Also scattered upon the 
slopes and among the debris where these reddened strata exist, 
there are frequently to be seen masses of slag, such in appear- 
ance as results from furnace fires or from the consumption of 
impure coal. Much of it is plainly seen to consist of partially 
fused rock, and masses are common which have the appearance 
of true volcanic lava; to which source indeed many persons 
have believed them due. 
r. Hayden made mention of these phenomena in his re- 
rts a others have done the same to some extent; but 
probably the fullest and best description of them that has ever 
been published was given by Mr. J. A, Allen in the Proceed- 
ings of the Boston Society of Natural History, volume xvi, 
pages 246-262. 
rofessor James D. Dana has also some important remarks 
upon the subject in his Mineralogy (1880), page 763; but my 
object in again calling attention to this subject is to make so some 
suggestions as to the one of these fires and the time within 
which they have taken place. 
During my examination of the Laramie Group in North- 
eastern Montana last summer I had good opportunities for 
