

woArtieh VIT. 
CONDITIONS OF DEPOSIT CRETACEOUS AND TERTIARY. 
BURNING OF LIGNITE BEDS.—COMPOSITION AND ECONOMIC 
VALUE OF LIGNITES AND IRONSTONES. 
CONDITIONS IMPLIED BY CRETACEOUS AND TERTIARY DEPoSITS—Period of shallow 
water—Extent and nature of submergence during Niobrara period—Detrital 
beds of Fort Pierre group—Closing period of shallow waters—Extensive land 
areas during Lignite Tertiary—Conditions of formation of lgnites.—-Com- 
BUSTION OF LIGNITE BEDS— Appearances indicating this action — Effects 
produced on surrounding beds—Area over which similar phenomena have 
been observed—Question whether such fires are spontaneous—Extent to 
which lignites have been destroyed.—CoMPosITION AND EcONOMIC VALUE OF 
LIGNITES AND [RON orES—Analyses of lignites—Nature of lignites—Classes 
of hgnites represented —Vaniability of water content—Lignites as fuels — 
Import of the St. Mary River coal—Other similar fuels near the mountains— 
Area of lignite-bearing formation—lIronstones of the Lignite Tertiary—Iron- 
stones of the Cretaceous—Probability of their future economic importance. 
Conditions implied by the Cretaceous and Tertiary Deposits—Nature and 
Origin of their Material. 
378. The question of the origin of the material composing the Cre- 
taceous and Tertiary rocks of the interior continental region, is one of 
considerable interest. The general aspect of the beds of the first and 
second divisions of the formation, is that of shallow-water deposits, They 
consist largely of sands, and coarse detrital materials, and, from the fre- 
quent occurrence of land-plants, and the occasional preservation of fresh- 
water molluscs, in both their eastern and western developments, argue the 
neighbourhood of considerable areas of dry land. The third, or Niobrara 
division, in the eastern portion of the area, consists in great part of the 
calcareous remains of molluscs, foraminifera, etc., and resembles the accu- 
mulation of a somewhat deep sea, from which cold arctic currents were 
excluded, and into which very little detrital matter was being carried. A 
general depression of the present surface of the continent, to the extent 
of about 1,500 feet, would give a depth of 700 to 800 feet, above the hori- 
zon of the Niobrara deposits ; and would be amply sufficient to satisfy the 
conditions indicated by their animal remains. A depression of this ex- 
tent, would however, almost submerge the Laurentian barrier to the north 
and east, and would suffice in its present condition to open broad avenues 
