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1 
188 B. N. A. BOUNDARY COMMISSION. 

provisional only.* In the same report the position of the Coalville 
lignite series is admitted as doubtful, the uncertainty being caused, 
however, by the local disturbances of the strata, the beds of Cretaceous 
No. 2 appearing to overlap them, The conclusion arrived at is, how- 
ever, that the coal is probably in reality ‘ above the black Cretaceous 
clays of No. 2, and forms a part of the Upper Cretaceous group.” + 
On another page of the same report it is stated that while in some 
localities the line between the Cretaceous and Tertiary is well marked 
by the absence of ine and brackish- 
water aspect—that in others, as in the Bridger Pass district, the division, 

however minutely the beds may be studied, must always be an arbitrary 
one.{ In 1872 Dr. Hayden is fully prepared to admit the Cretaceous 
age of a great part of the series. He considers the evidence of the 
Cretaceous age of the lower coal beds in Utah, especially at Bear 
River and Coalville, to be conclusive, and writes: “ But if we admit 
that the coal beds of Wyoming and Colorado are all of Cretaceous 
age, I think we may extend them all over the North-west and ignore the 
evidence from the fossil plants entirely. The facts, as we possess them 
at the present time, seem to point to the conclusion that the lignite strata 
commenced during the latter portion of the Cretaceous period, and con- 
tinued on into Tertiary times without any marked physical break, so 
that many of the Cretaceous types, especially of the vertebrata, may 
have lingered on through the transition period, even into the Tertiary 
epoch.”§ Also, in speaking of the lignite-bearing strata of the region of 
the Gallatin Valley: “The evidence at the present time points to the 
conclusion that the lower portions of this group are Cretaceous, passing 
up by gradual transition into the Tertiary, and that the greater portion 
may be regarded as of the age of the latter period.” In the maps and 
sections published with some of the reports referred to, the Tertiary 
classification of the beds in question is adhered to.|| Professors Hitch- 
cock and Blake have also adopted Dr. Hayden’s colouring in their general 
Geological map, bearing date 1872. 
Dr. Hayden’s explorations were begun on the eastern margin of the 
formation, but previous to 1857 he had examined the country bordering 
the Missouri as far west as Fort Benton, and on the present line of the 
Pacific Railway, to Green River. 

* U.S. Geol. Surv. Territ., 1870. p. 73 t Ibid.,p. 157. t Ibid., p. 76. 
§ U.S. Geol. Surv, Territ., 1872, p. 14. 
|| See Map and Section illustrating Geol. structure of. Country bordering the Missouri, 1857. Map 
accompanying Yellowstone and Missouri Report, 1869. Map accompanying final Report on Nebraska, 1872, 
‘ & 
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