Mill Bridge Series.
“On making its exit at the eastern end of Gopher Bridge, Cougar creek pours down a narrow rock-cut for a distance of 350 feet, when it again disappears in a whirl of flying spray below the surface of the valley. It reappears, 300 feet farther on at the bottom of a deep gorge, having dropped 85 feet while underground. The interval between the exit and entrance has been named Mill bridge by the party previously mentioned, on account of the roar of the water as it rushes underground through the choked entrance, resembling the noise made by a big mill in full operation.
“The rock-cut above referred to is narrow, about 8 to 10 feet wide, and of regular appearance. The upper half presents a series of cascades and falls, and the sides show curious small potholes that are in the process of erosion from the soft limestone. It has been named ‘The Flume,’ owing to its resemblance to a millrace. There are several openings at the point where the creek disappears, and its last spectacular leap as it vanishes underground is very striking. 70 feet farther east is a larger opening, at one time the point where the stream disappeared, but as the rush of water cut deeper in the rock channel it took advantage of a handy crack and gradually carved out for itself the opening where the full volume now descends.
“About the centre of the flume, on the eastern side, and 30 feet from it, is the entrance to the Mill Bridge series of the caves, shown on the [map] as ‘Entrance No. 1.’ This entrance is a mere cleft in the rock strata, and is only wide enough to admit of the passage of a man’s body. The total length of the underground passageway, at one time accommodating a very considerable volume of water, is 400 feet. The height varies from a minimum of 10 feet to a maximum of 25 feet, and the width from 3 to 15 feet. At its eastern end it opens to an irregularly-shaped chamber of approximately 60 by 70 feet, with a greatest height of 20 feet. This chamber has been named ‘The Auditorium’ by the first exploring party. Cougar creek in its flow beneath Mill bridge passes through the Auditorium, and as it falls 75 feet in a distance of 200 feet, from its entrance beneath Mill bridge to the Auditorium, the chamber is replete with its roar, and the name is appropriate, though hardly in the conventional sense of the word. Faint daylight enters through the passageway of the waters and serves to make the surroundings look dim and mysterious. The frosts of winter also reach this spot, and in the spring stalactites and stalagmites, formed of huge icicles, are seen in columnar groups surrounding the dashing waters and extending some distance into the chamber itself. In this particular spot disintegration has created much havoc and the walls no longer show the marks of water erosion, while the floor is heaped with rock debris fallen from the ceiling. The passageway, however, that connects it with the surface is still intact as a sample of the power of water erosion. It is composed of a series of potholes, connected one with the other by short narrow passages. The bottom of each succeeding pothole, as you recede from the entrance, is at a lower elevation, sometimes as much as ten or fifteen feet. To make access possible, Deutschman has, with the assistance of a bridge carpenter loaned by T. Kilpatrick, superintendent of the Canadian Pacific Railway Company at Revelstoke, placed rough ladders from floor to floor. Most of these potholes hold water in the hollows at the bottom, and, in one case, the water is so deep—4 or 5 feet—and the potholes so wide that a floating bridge had to be built. When it is realized that every bit of timber used in these constructions had to be hewn from the tree and transported on the shoulder or back, over a road hardly accessible for a mountain goat, to the place where it was utilized, some idea of the magnitude of the work can be formed.
“At one spot the passageway twists in a loop, and here the potholes are of such a curiously spiral form that it has been named ‘The Corkscrew.’ Across this bend, about 12 feet above the main floor, a gallery extends for 120 feet. It is of a similar pothole formation, but on a smaller scale than the main passageway. Directly below it, at the lower end, is a peculiar sharp spike of rock that has evidently been subsequently carved out by water pouring from this gallery, as is readily shown by the erosionmarks on the component rocks. In addition to the lines of erosion on the rock spike and in the gallery pothole, honey-combing is seen on the right and high up on the left and, still farther on the left, spatulated markings to the depth of half an inch, or a little over, which is a very common feature in all three series.
“Throughout the Mill Bridge series, with the exception of the Auditorium, the floors and ceilings are of water-worn rock, and practically no debris has fallen away pointing to the fact that this channel is of more recent origin, and the rock through which it has worn of a more compact stratification.
“At one time it was reported that the roof of this passage was set with sparkling quartz crystals. It turned out, however, that they were only drops of water that had collected through leakage or condensation. Some of the potholes are very curiously marked by thin incrustations of carbonate of lime spreading over their concave surfaces in florescent patterns. Overhead in many places are seen projecting spurs that have withstood the action of the water owing to superior hardness, or that, through some deflection of the current, have not had the same force brought to bear upon them. The waters of Cougar creek are derived from the melting glaciers and snow deposits lining the sides of the peaks enclosing the valley and, in consequence, carry a considerable quantity of sediment, composed of very fine rock particles. The quantity of sediment carried would, of course, be greatest when the stream was at flood stage. This sediment has doubtless been a factor of much importance in the erosive power of the waters, and a residue may to-day be seen as a very thin mud-coloured coating on the walls and floors of the passageways, where it has been deposited by the subsiding waters. At a very high stage of water in the creek there was an overflow into Entrance No. 1 that made the first exploration by W. S. Ayres and party a wet and somewhat dangerous operation. This overflow, however, was dammed back by Deutschman, and no further trouble has since been experienced with it.