128 GEOLOGICAL SUEVEY OF THE TESRITOEIES. 



Creek, Mr. Marshall has gathered and taken oot more than 500 tons of 

 this ore. In smelting it in a small blast-furnace, with i3ure charcoal 

 from the mountains, the following mixture was used : Ore, 200 jDounds ; 

 limestone, 20 pounds ; charcoal, 13 to 15 pounds. Smelted in this way, 

 4,400 ijounds of ore produced one ton of a very excellent quality of gray 

 pig-iron. 



POST-LIGNITIC POEMATIOiN^S. 



In the lignitic we have the uppermost of those sedimentary formations 

 which participated in the folding and upturning of the rocks along the 

 mountain front, while it is also the last extended formation with which 

 we have to deal east of the mountains. The remnants of but one group 

 of sedimentary rocks is here found which is more recent than the lig- 

 nitic, and that is quite subordinate both in extent and importance. 

 Opportunity was not had to study it particularly, but the impressions 

 received from what was seen of it will be briefly stated. These beds 

 usually consist of gravels, often exceedingly coarse, which are derived 

 principally from the archeean rocks of the mountains, and consist mostly 

 of hard quartzite, schist, and granite dShris. They always lie nearly or 

 quite horizontal, apparently entirely undisturbed, frequently nearly 

 cover the upturned edges of the older folded strata, occasionally almost 

 lapping over them on to the metamorphic rocks of the mountain spurs, 

 and stretch eastward into the plains in well-marked terraces. Their 

 thickest development is naturally nearest the mountains from which 

 they were derived, though they probably nowhere reach a thickness of 

 500 feet, perhaps not half that amount. The main cross-valleys nearly 

 always cut through them to the lignitic or cretaceous beds beneath, 

 though the latter are generally concealed by debris or alluvium of the 

 streams. They seldom comjDletely cover the highest portions of those 

 ridges capped by Cretaceous No. 1, and, at the north, where the zone of 

 hog-backs is wide and these ridges lie some distance from the mountains, 

 the gravels are forced out eastward equally far. From the gently-slop- 

 ing tops of No. 1 or No. 3 they here extend eastward for several miles as 

 low terraces, as near the Thompson and Saint Vrain Creeks. Near the 

 latter some yellow marl occurs above the gravels, the latter being cement- 

 ed largely with oxide of iron. The benches or terraces here seldom 

 reach an altitude of more than 200 or 300 feet above the streams, often 

 break off quite abruptly at their ends, with occasional outlying "table- 

 mountains," lower terraces showing here and there, while the main ter- 

 race is in places separated from the hog-back ridges at the west by a 

 small north and south valley. Between Left-Hand and Boulder Creeks 

 a large area has been removed, leaving a shallow, fertile valley. In 

 proceeding southward the lower folded beds, assuming a steeper eastern 

 dip, occui^y a much narrower zone than at the north, and the terraces, 

 likewise, lie close ux^ under the mountain-spurs and reach greater alti- 

 tudes. They have, perhaps, a typical development between the North 

 and South Boulder Creeks. It is here that the Triassic sandstones rise 

 to their greatest height in the formidable ridge cut midway by Bear 

 Caiaon. Passing from the sandstones over hardly more than 2,000 feet 

 of outcropping Jurassic and lower Cretaceous beds, we pass directly 

 from No. 3 upon the high gravel terrace. Boulders of the red sand- 

 stone, over 10 feet in diameter, may here be seen, and the mass through- 

 out is of exceedingly coarse material, in which sandstone boulders pre- 

 dominate. For a quarter of a mile outward the inclination of the surface 

 is about 50, gradually becoming flatter, until, in less than a mile, the 

 abrupt slope is reached which descends to the valley of the South Boul- 



