The Fort Union Format ion. — Weed. 209 
Seen from below, the exposure shows three prominent seams 
of lignite, whose dark lines are everywhere noticeable in the 
adjacent bluff exposures. Ex-:imined in detail, the series in- 
cludes at least five other seams which are from 1 to 2 feet in 
thickness, but which are covered in the exposure by the wash 
of the silty, intervening beds. The section was made about a 
mile west of Willow station. 
Section of the north bin f of the Missouri river, near the month of the 
YeUoicstone. 
Feet : 
5 Sandy, buff colored beds alternating with gray beds, 3 to 5 feet 
in thickness. The general appearance of the upper part of the 
bluff is that of a smooth, clay slope, as the silty wash from 
above partially obscures the outcrops of the strata. 
7 Gray and ash-colored clays carrying fresh-water shells, the out- 
crop showing a cracked and muddy surface. 
1 Lignite (?) seam. 
3 Limestone; yellowish in color and breaking into small, angular 
bits, the largest -^j^" in diameter. The horizon is inconstant, 
the limestone really forming a lens. 
4 Arenaceous clays, buff in color and forming the summit of a 
prominent bench that circles the fjluff. 
Ik Gray shale, carrying shell remains. 
2 Lignite seam, impure and weathering to a fine Carboniferous 
clay. 
i Gray shale. 
5 Lignite seam, overlain by flaky, laminated shale, carrying shell 
remains. 
If) Argillaceous, ashy gray shales, weathering into a silty wash. 
(5 Light colored bed, whose outcrop is covered with an alkaline ef- 
florescence and with the brittle, shreddy fragments of limestone 
from the weathering of a concretion of this material, whose 
surface is of a rich terra cotta color. The base of this zone 
forms a platform terrace that is 6 feet wide, 
lo Sandy beds, .soft, reddish l:)uff in color, resembling a silt in ap- 
pearance and weathering with a pitte^l surface. 
25 Loosely cemented sands with concretions, illustrated in the pho- 
tographs (C. D. W., 1895). Those concretions have all shapes 
and sizes, up to G feet in diameter. The bed forms a marked 
sandy layer, but is not hard enough to weather as a ledge. 
The fossil plants collected from the Williston locality show- 
only one species, Onoclea sensihi/is Linn., /"o.v.s/Z/.v Newb. The 
shells obtained from the section just given are of fresh-water 
species and are of forms common to the Laramie and Fort 
Union beds. They have been identified by Mr. Stanton as 
Viviparns trochiforniis M. tt H., I'. Icai M. ct H., and frag- 
ments of Uilio s]t. 
