The Fort Union Formation. — Weeil. 203 
The name Fort Union, applied to the Fort Union beds, was 
afterwards extended by Hayden to include all the lignite- 
bearing bed? of the Northwest, for which the term Lignitic 
group* was afterwards used. 
By agreement with Mr. Clarence King, the term Laramie,f 
used for the prominent coal-bearing horizon of the region of 
the 40th parallel, was accepted by Hayden, who extended it to 
include all of his Lignitic group, and he included in this all 
the lignitic strata of Montana. Explorations in the upper 
Missouri region by C. A. White and L. F. Ward in 1881-3, T. 
W. Stanton in 1894, and at various times from 1884 to 1895 
by the writer, have shown that the lignite or coal seams of 
this region are of very different age, the oldest being Lower 
Cretaceous (Kootanie). A higher horizon. Belly River beds, 
occurs in the middle part of the Upper Cretaceous series, and 
other commercially available coal beds are found in the Fox 
Hills, in what is now discriminated as true Laramie, and in 
the upper series which the author has for some years tenta- 
tively designated as Fort Union beds. It is therefore evident 
that the Lignitic group of Hayden comprises strata of very 
different age and relations, and that the application of the 
term Laramie as its equivalent has misled some investigators 
into a fundamental error that has vitiated conclusions reached 
in the discussion of the relationships of the Laramie, based 
wholly or in part upon the facts gathered in the upper Mis- 
souri region. 
Livingston fonnation. — In pursuance of the geological work 
of the U. S. Geological Survey in Montana, in has been the 
duty of the writer to map the areal geology of some 10,000 
s(juare miles along the eastern border of the Rocky mountains, 
and to make a reconnaissance of other parts of the state. In 
the course of this work it soon became apparent that the use 
of the term Laramie group would have to be restricted tc) des- 
ignate the series of brackish and fresh-water beds, usually 
coal-bearing, which terminated the Cretaceous. This distinc- 
tion, which accords with the original definition and usage of 
the word, was necessary because it was found that, while per- 
fect conformity apparently existed throughout the strati- 
*Pr()c. Acad. Nat. Sci. Phila., vol. xviii, p. 1.3.3, Dec. 1861. 
tU. S. Geol. Explor. 40th Parjillel, \i>\. i. p. a31. 
