70 GEOLOGICAL SURVEY OF THE TERRITORIES. 



range), but on the slope between li and i, I came suddenly upon the 

 well-known sandstone of No. 1 Cretaceous, lying beneath the Paleozoic 

 rocks and to all appearances conformable with them. Keeping on at right 

 angles to the dip, I passed first over the outcropping edges of Jurassic 

 and Triassic (?) rocks ; then over a ridge of Carboniferous conglom- 

 erates and limestones, much crushed and metamorphosed ; and finally, 

 beneath these still, over a full but much distorted series of Triassic, Juras- 

 sic, and Cretaceous rocks. The dip rises in places to 70 and 80 degrees, 

 and the strikes are not quite uniform. I was at first entirely unable to 

 account for this extraordinary succession of strata, and did not succeed 

 in solving the problem until I had followed the outcrops across the valley 

 to the south and discovered in the higher ridge at j the arch of the fold, 

 which, on the opposite side of the valley, had been carried away. 



It seems that in the first place a great fault occurred, in which there 

 was a throw sufficient to place the Lower Cretaceous of the west side 

 opposite the Lower Carboniferous of the east side, and that a powerful 

 lateral movement had then driven the opposing strata together, the 

 harder Carboniferous rocks sliding forward upon the upper surface of 

 the quartzites of the Dakota group, and at the same time bending them 

 and portions of the firmer substrata back in a sharp fold, which, from 

 the continued pressure, has been carried en masse beyond the vertical and 

 almost severed below by the immense pressure. (See section F, large 

 sheet.) In the next ridge south, at,;, the fold is not so abrupt, and the 

 ridge m, facing White Eock Creek, there is only a gentle arch of the 

 strata (see section Gr, large sheet), while a considerable gap occurs 

 between the faulted strata in which the granite appears. 



At n the infolding ceases, and in the valley at o the strata dip some 

 forty degrees to the west (section H, large sheet). Toward p they rise 

 again to the vertical, and at q have been pushed back to forty-five de- 

 grees past the vertical by a mass of granite, which now lies superim- 

 posed upon the ridges like so much trachyte. 



Before reaching the bed of Teocalli Creek, at r, the strata fall back 

 again almost to the normal horizontal position. 



Here the fault forks ; one branch extends southward through s, and 

 the other turns eastward along the north face of Teocalli Mountain and 

 continues in a pretty direct course to station 3. 



The elevation on the north side of this branch of the fault has been 

 very great, and has extended over a large area. White Eock and Am- 

 phitheater Mountains have probably been the highest granitic points, 

 but the whole mass of the Castle group has been carried up so uniformly 

 that the Paleozoic rocks lie in an almost horizontal position upon a 

 plateau-like mass of granite. (See section H, large sheet.) 



A few miles south of station 3, which is the most southeasterly gran- 

 ite outcrop of the Castle group, a small pyramidal mass of granite has 

 forced its way up through the primordial rocks bordering the granites 

 of the Sawatch range, producing the summit of Italian peak. Although 

 this bit of granite seems quite isolated from the previously-described 

 centers of disturbance, a very marked line of fracture and faulting may 

 be traced between it and the Castle group, but as the details of this 

 region have already been given by Drs. Hayden and Peale, I shall con- 

 tent myself by giving, in conclusion, a brief recapitulation of the more 

 striking features of the Elk range. Topographically speaking, it is a 

 spur of the great continental divide, but geologically it is quite inde- 

 pendent in origin. It trends nearly northwest and southeast, so that 

 one extremity lies high upon the slopes of the Sawatch range, while the 

 other extends far out into the low country bordering the Grand Eiver. 



