FLORA OF THE MONTANA FORMATION. 
By Frank Hall Knowlton. 
INTRODUCTION. 
The history of the so-called Laramie and allied formations of the 
Rocky Mountain region has been an intricate and interesting one, and 
much literature exists on the subject. As summaries have recently 
3een presented l it is deemed unnecessary again to go over this ground, 
except in the briefest manner and in so far as it is essential to an 
mderstanding of the reasons for separating the present paper from my 
contemplated monograph on the Laramie floras. 
The series of strata which has in recent years been known as the 
Jaramie group or formation, was first called the Lignitic group and 
vas believed to contain all the coal of the region in which it occurs. 
Che Lignitic also included certain lower Tertiary beds, now known as 
he Fort Union beds, and the whole was at that time regarded as 
tertiary in age. Later the Laramie was differentiated as a single 
ormation, by Mr. Clarence King 2 and Dr. F. V. Haydeu, and charac- 
erized as the uppermost division of the conformable Cretaceous series, 
,nd the Fort Union was ultimately associated with the lower Tertiary, 
although still regarded by some as belonging to the Laramie series. 
Ls thus defined, the Laramie was thought to be very sharply circuin- 
cribed, but later investigations have shown that this view requires 
lodification. Thus it was found that instead of being uniformly under- 
lin by marine Cretaceous, certain of the coal seams were intercalated 
1 marine beds, or, in other words, there had been alternations of 
esh and brackish or salt water before the true Laramie age prevailed, 
'he evidence for this phase of the subject will be more fully presented 
i 1 the following pages. 
As investigation progressed it became evident that certain beds of 
ae upper portion of the Laramie series could not be satisfactorily 
armonized, and this led to the separation of the Arapahoe and Den- 
'Ward, Synopsis of the flora of the Laramie group: Sixth Ann. Rept. 0". S. Geol. Survey, 1884-85, pp. 
9-557, P18.XXI-LXV (1886). 
White, Correlation papers— Cretaceous : Bull. IT. S. Geol. Survey No. 82, pp. 140 et seq. (1891). 
J See U. S. Geol. Expl. 40th Parallel, Vol. I, p. 331 (1878) . 
Bull 103 1 1 
