The Fort Union Formation. — Weed. 205 
cally distinct and readily differentiated from the somber 
colored sandstones of volcanic material composinj^ the Living- 
ston beds. The plant remains from these beds are not of 
Laramie nor of Denver bed types, but are species character- 
istic of the strata in the vicinity of Fort Union, and that 
name is therefore adopted for the formation. As will be 
shown later, the formation is one of widespread extent in the 
plains country of Montana, and it extends northward into 
Canadian territory. 
The Fort Union formation as developed in the Crazy moun- 
tains consists of a series of alternating sandstones and gray 
clay-shales, the latter holding limestone concretions often 
many feet in diameter at various horizons. The sandstones 
are usually light gray in color, loose-textured, and frequently 
crumbly, cross-bedded, and often hold round cannon-ball con- 
cretions which are merely indurated sandstones. The grains 
are generally water-worn and rounded fragments of quartz, 
more rarely of feldspar, and are of gneissic origin. The 
character of the quartz and the abundance and nature of the 
feldspar fragments diifer markedly from those normal to the 
underlying Livingston beds. The clay-shales are sometimes 
calcareous, generally gray in color, weathering into fine, cubi- 
cal debris. The limestones are dense and flint-like, breaking 
witli conchoidal or splintery fracture. They are gray but 
weather with light earthy brown surface, and are sometimes 
fossiliferous. Lignites occur rarely, are impure, friable, and 
of little economic value, differing every way from the coals of 
the Laramie. 
A continuous section measured at the base of the mountains, 
embracing marine Cretaceous (Montana group), Laramie, 
Livingston, and Fort Union beds, is given below : 
Section of Strata foi-ming Eastern Footslopes of the Crazi/ Moitntnins, 
oil Lebo Creek. Montana. 
Feet. 
880 Sandstones ; light colored, generally brownish or buff, of vary- 
ing coarseness, texture, and hardness; in thick and thin beds, 
sometimes cross-bedded and often fissile. 
7.55 Alternating series of sandstones and shale : the latter gray, 
argillaceous, not laminated, weathering in smooth slopes 
with fine cubical debris and frequently holding large and 
small limestone balls and ovoids. These consist of dense and 
hard, flinty gray limestone, generally checked ;uKi cracked. 
