BASA L CONGLOMERATES. 



85 



Sometimes the bowlders or cobblestones forminj^ the conglomerate are 

 of considerable size, from one to four feet in diameter. One of the best 

 exposures of this character was seen in the canon of lower Rapid (Jreek, 

 and is illustrated in the annexed illustration. 



The large bowlders shown at the biise of the section are perfectly water- 

 rounded and form a broad talus extending to the bed of the creek. They 



appear to have had no cementing material, but lie as 

 loosely as if they had been dumped from a cart. 

 This is apparently but a local accumulation; at a 

 short distance on either side no bowlders are visi- 

 ble, though the underlying slates are still exposed 

 to view. 



A similar heavy conglomerate formation is found 

 in many other parts of the Hills, as, for instance, on 

 the headwaters of Box Elder Creek, where a bowlder 

 or cobblestone conglomerate with fragments two feet 

 or more in diameter, rests upon the upturned edges 

 of the ArcluEan quartzites and slates. 



In some places a conglomerate is found above 

 (lam siuuistonc on lower the basc of the formation, in which the pebbles seem 



Rapid Creek, showiiif; tlio '■ 



bowlders at its base and ^o liave bccu formcd froui ijreviousl V cxistiuj? portions 



Its nnconiorniity willi the. ^ •' '-'■'• 



thi'cknes""s(R)'f'e*et' ^°^'^' ^^ ^^^^ saudstonc. A good example may be seen near 



1. Massive jjray limestone the eastern basc of Terry Peak. Near Terry Peak 



(Carbonil'iMons). 



2. Thinbediied imimre lime- also Potsdam Conglomerate was found so thoroughly 



stone (Carboniferous). 



:i. Keddish sandstone (Pots- mctamorplioscd that a fracturc could be made as 



dam). ^ ^ 



4. coneeaied cnsilv across tlic Quartz pebbles and bowlders as in 



i). Coai'se reddish sandstone ■' ^ '■ 



(Potsdam). any Other direction, the silicious cement beinff changed 



0. Loo.sebowlders(Potsdam). J ' o o 



7. scbusts (Arebaan). Jj^|.q q^^artzite as hard as the quartz pebbles themselves. 



The cementing material of the conglomerate is generally silex, and this 

 is reinforced by the oxide of iron. Carbonate of lime also has been found 

 in many localities, and in such cases the interstices are more j)erfectly filled 

 and the conglomerate is more compact. The calcareous cement often con- 

 tauis the remains of fossils and grains of glauconite. As has been observed, 



Fig. 10.— Scetioii of the Pot,- 



