2S GEOLOGICAL SUEVEY OF THE TERRITORIES. 



tendency of the mountain-ranges. It extends out tangentially several 

 miles from the base of the main range into the plains between Little 

 Thompson and the north branch of Saint Vrain's Creek. Just as the 

 Saint Vrain emerges from the Hogbacks in the plains, the valley ex. 

 pauds to a width of at least five miles, (c,) so that there is only this 

 main ridge or spur between the drainage of the Little Thompson and 

 Saint Vrain's Creek. This ridge is also partially domed over, although, 

 a portion of the Upper Cretaceous beds incline away from the ridge on all 

 sides. On the east side an oval mass h as been removed through the quartz- 

 ites of No. 1 and the Jurassic group, just exposing the red beds in the bot- 

 tom of the depression. The quartzites stand up nearly vertical on the 

 east side, forming a semicircular wall, while on the west side the summit 

 rises 830 feet above the valley of Saint Train, with, a dip of only 20° or 

 30°. The layers of rocks are quite massive, 4 to 6 feet thick, composed of a 

 beautiful pudding-stone, the pebbles rounded and as smooth as glass. 

 There is here at least 10 or 15 feet of solid pudding-stone, and the peb- 

 bles all through it have the same elegant smoothness and are sometimes 

 an inch or two in diameter, but usually smaller. The depression as well 

 as the sides of tlie ridge are covered with huge cubical masses that have 

 fallen down. The last two smaller spurs do not appear to have inter- 

 rupted to any extent the trend of the ridges. On the north side of the 

 Little Thomjison and inside of the uplifted ridges the short rounded 

 schist-spur is distinctly seen trending northwest and southeast, which has 

 produced the puff. The oval opening (d) in the puff is about half a mile 

 wide and a mile long, produced by erosion. To one traveling between 

 the Hogback ridges and the granites these tangential movements of the 

 internal forces do not seem to have disturbed the symmetry of the prin- 

 cipal series of ridges. The Little Thompson in passing through, the 

 main ridges cuts them at right angles, and on the north side a fine, reg- 

 ular vertical section is shown, with the beds all in their normal position, 

 while on the south: side the same beds incline toward the north from 

 the ridge or puff that extends down into the plains, (well shown in sec- 

 tions 2 and 3.) The Little Thompson, after emerging from the sand- 

 stone ridges, cuts a deep channel through the calcareous shales of No. 3. 

 The bed is here 200 to 300 feet in thickness. These unusual develop- 

 ments of a group show the difllculty of obtaining the exact thickness 

 of these uplifted groups of strata at dilferent points with any degree of 

 accuracy. We may call this spur an oblong quaquaversal, for the beds 

 incline at greater or less auigles from both sides, and come around the end, 

 forming quite distinct semicircles. Nos. 1, 2, and 3 form distinct ridges 

 from the end of the spur, and the plains below show clearly that they 

 are underlaid by the softer materials of the Upper Cretaceous. On the 

 south side of the spur there is a triangular-shaped valley, through which 

 the north branch of the Saint Vrain flows from the base of the mountains. 

 The upper part of this triangle is a synclinal, as is so well shown in the 

 illustration. South of Saint Vrain's Creek the ridges begin to close up 

 rapidly, so that at Boulder Creek they form a narrow belt. Two or 

 three fragmentary ridges of Lignitic sandstone rise above the surface 20 

 or 30 feet, not over three miles from the foot of the mountains, and the 

 strike would carry them close up against the very base near Boulder 

 Creek. The coal- strata continue to approach nearer and nearer, until 

 between Boulder and Clear Creeks they form a portion of the foot-hills. 

 The terraces along the base of the mountain are very remarkable, and 

 will be noticed more fully in another place. As they are composed of 

 superficial deposits the ridges pass under them at times, and are hidden 



