13 



combustion of the lignite beds. By reason of the greater resistance which these altered beds 

 offer to erosion, the exposures are greatly diversified and are productive of those remarkable 

 features exhibited in the Roche Percee and in the characteristic aspects of the Bad Lands. 

 The lignite beds may have a thickness of from a few inches to eighteen feet, and they are 

 usually overlaid with a plant-bearing bed of clay. 



Dr. Dawson points out that in their eastern extension the lignite deposits show no trace 

 of marine or brackish water conditions, and whenever remains of molluscs are found, they are 

 those of fresh water (5,152.) From Roche Percee westward to Wood mountain, the deposits 

 are identical with the eastern fresh-water extension of the southern Lignite Tertiary or Fort 

 Union beds (6,154.) lint from Wood mountain westward the character of the formation 

 changes, until in the region of the buttes the appearance Js totally different. The introduc- 

 tion of the remains of reptiles adds a new feature, and in the Milk river fresh water forms 

 are mixed with marine Ostrea. In the Sweet-grass hills, Ostrea shells are found in great 

 abundance, together with molluscs identical with those of the Bitter Creek Coal series of 

 Wyoming, and aDo^tia, probably the same as those from Coalville, Utah. Although there 

 is a reversion to fresh-water forms near the first and second branches of the Milk river, the 

 general tendency is towards salt water conditions eastward — the former spread eastward in the 

 lower layers as far as Roche Percee, while the latter spread westward in the upper beds, nearly 

 to the base of the mountains. 



Dr. Dawson closes his account with the conclusion that the Tertiary beds of the Forty- 

 n^nth parallel are identical with those of the Judith River formation, " the age of which has 

 long been an unsettled question, and they have only lately been included by some geologists 

 with the remainder of the Liy;nite Tertiary and called Cretaceous Dr. Ifayden was only 

 prevented from calling them Fort Union Tertiary by the occurrence of certain vertebrate 

 remains, the meaning of which is now better understood" (6,157). 



CALGARY AND COCHRANE, ALBERTA. 



Cochrane, Alberta, lies on the western edge of the Laramie basin, about six hundred 

 miles northwest of Roche Percee, while Calgary is about twenty-five miles to the southeast 

 of the former. As the formation in these localities is the same as for the more southern 

 portions of the basin, no further discussion is required in this connexion. 



Very few plants have been collected from either of these places. Penhallow (74, 57) 

 has recorded tvi^o species of wood from Cochrane, one of which is a species of Thuya, probably 

 T. interrupta, which is found abundantly through the Tertiary of the western provinces. The 

 other is a species of Taxodium which has been designated as T. laramianum, but it is quite 

 probable that it may be the wood of T. oecidentale, a species very common to the Lignite 

 Tertiary. 



From Calgary, Sir William Dawson has obtained nine species (26, 15-18) as follows : — 



1. Platanus nohilis, Newb. 



2. raynoldsii, Newb. 



3. Populus acerifolia. Newb. 



4. cordifolia, Newb. 



5. ge7ietrix, Newb. 



6. Sassafras burpeana, Dn. 



