GEOLOGIC SECTIONS AND THEIR COMPOSITION. 



43 



Numbers 3 and 4 of this section are believed to represent the Sas- 

 katchewan gravels, while number 2 may be either the lower or upper 

 boulder-clay of the plains. Less than a mile to the northward the boul- 

 der-clay was observed to rest directly upon the Laramie rocks, numbers 

 3 and 4 having, run out. Number 4 has in some places a clayey matrix, 

 thus beginning to assume the character of the '' western " boulder-clay. 



About two miles further north, along the North fork and well behind the 

 southern part of the Porcupine hills (elevation about 3,900 feet), another 

 section was examined, of which, however, the total thickness remained 

 indetermined because of slides in the bank. This again shows boulder- 

 clay of a somewhat earthy and soft character, but containing many stones, 

 derived from the mountains or adjacent foothills. The limestone peb- 

 bles are often distinctly but very lightly striated, and have apparently 

 been well rounded by ordinary water action before the striation had been 

 added. Two small crumbs of Laurentian material were discovered by 

 search on the face of this exposure, but the decrease in importance of 

 such material in the boulder-clay to the westward and where sheltered 

 by the high ridges of the Porcupines is very apparent. 



The comparatively soft and earthy character of the boulder-clay seen 

 behind the Porcupine hills was generally observable. 



Reverting to the main line of approach w^hich we have been following 

 toward the mountains, an exposure on the South 

 fork of the Oldman, examined in 1883, may next 

 be alluded to. This is distant from the moun- 

 tains about 12 miles, with an approximate ele- 

 vation of 3,700 feet. It again shows a boulder- 

 clay, similar to the last, overlying a few feet of 

 gravel derived from the mountains. Both de- 

 posits occupy a hollow, possibly that of an old 

 river valley, as shown in the diagram annexed. 



In 1881 another section was noted on Mill 

 creek, still nearer to the mountains (six miles 

 distant, elevation 3,817 feet), which showed 

 boulder-clay of the usual character underlain 

 by a very hard boulder-clay or till of different 

 aspect, below which was a few feet in thickness 

 of fine, compacted gravels. Some Laurentian stones were found on the 

 surface in this vicinity above the level of the section, but none were seen 

 in it. A similar instance of bouldery clay overljdng thin layers of gravel 

 was discovered in the same year high up on Pincher creek, in this neigh- 

 borhood, within a couple of miles of the actual base of the mountains. 



The two last mentioned localities are within the limit of the country 



^^^^^^^^-l 



Figure 2. — Section on the South 

 Fork of Oldman River. 



A = Laramie (Willow creek) 

 beds. 

 B = Saskatchewan gravels. 

 C= finely stratified clays. 

 D = boulder-clay. 

 E = surface gravel. 

 F= soil. 



Base of section 25 feet above 

 present river-level. 



