potholes in the making. Other small openings occur where the stream descends in the cloud of spray. Seventy feet further east is a larger opening, which was once its entrance; but as the stream cut deeper in the rock-channel, it utilized a handy crack and gradually carved out sufficient ingress for its full volume.
Thirty feet easterly from the centre of the Flume is another opening to the Mill Bridge Series, called on the map "Entrance No. 1," a mere cleft in the rock wide enough to admit a man's body. The total length of its passageway, at one time accommodating a considerable volume of water, is 400 feet. Its height is from 10 to 25 feet, and its width from 3 to 15 feet. It leads to an irregularly shaped chamber. named the Auditorium, of approximately 60 to 70 teet with 20 feet of greatest height. Cougar Brook passes through it and, as it falls 75 feet in the distance of 200 feet from its ingress at Mill Bridge to the Auditorium, the chamber is full of sound and fury. Faint daylight enters through the passageway of the waters, making the place look dim and mysterious. Here the frosts penetrate and in spring stalactites and stalagmites of icicles in columnar groups surround the torrent and extend some distance into the chamber itself. Disintegration has made such havoc that the walls no longer show marks of water-erosion, and the floor is heaped with rock-debris fallen from the ceiling. The connecting passageway, still intact and a good example of erosion, is composed of a series of potholes connected by short corriders. From the entrance, each succeeding pothole is lower, sometimes by 10 or 15 feet. There are rough ladders placed from floor to floor. Most of the potholes here hold water, one to a depth of 4 or 5 feet and so wide that a floating bridge is necessary. When the Caves were first open to the public, all the timber used for construction had to be hewn from the trees and carried on the shoulders over places scarcely accessible to a mountain goat.
A loop in the passageway is called the Corkscrew, from the curiously spiral form of the potholes within it. Across this bend about 12 feet above the main floor, a gallery of pothole formation on a smaller scale extends for 120 feet. Directly under it? lower end is a peculiar sharp spike of rock evidently chiselled by water pouring from the gallery. Component rocks show similar erosion.
With the exception of the Auditorium. the floors and ceilings of the Mill Bridge Series are of water-worn rock; and practically no debris has fallen, showing this channel to be of more recent origin. Some of the potholes are incrusted with carbonate of lime in florescent patterns. In places overhead are projecting spurs that have either withstood the erosive power of the waters or else escaped them by some deflection of the current. It is to be remembered that Cougar Brook, deriving its waters from the glaciers and deposits of snows on the peaks enclosing the valley, carries a strong erosive factor in the rock-particles which compose the glacial sediment.
The Gorge Series: From under Mill Bridge, Cougar Brook reissues to flow through an open gorge 80 feet below the floor of the valley and running at right angles to it. The forge is 300 feet long, about fifty feet wide, and is spanned by two natural rock-bridges. Its sides are composed of badly shattered limestone. At the lower
