THE BELT FORMATIONS
ALTYN FORMATION. This is the oldest of the several formations and thus occupies a stratigraphic position at the base of the entire series. It is composed mainly of sandy dolomites (magnesian limestones) and limestones which weather to a light buff color. It outcrops all along the base of the eastern front of the Lewis Range and comprises the entire block of Chief Mountain. Because of its comparatively great resistance to weathering and erosion it usually forms a conspicuous ridge or terrace wherever it crosses a valley. In the Swiftcurrent Valley it forms the dam which holds in Swiftcurrent Lake and creates Swiftcurrent Falls. In Two Medicine Valley the highway crosses a similar terrace which gives rise also to Trick Falls. In the St. Mary Valley it creates the Narrows and forms the imposing wall in lee of which East Glacier Campground is located. The rock of this formation can best be examined on the ridge immediately east of Many Glacier Hotel (between hotel and parking lot) and above Swiftcurrent Falls. Its average thickness is about 2,300 feet.
APPEKUNNY FORMATION. Lying on top of the Altyn are 3,000 or more feet of prevailing greenish shales and argillites* comprising the Appekunny formation. Slabs of these rocks, because of their great hardness have been used as flagstones in the walks at the Many Glacier Ranger Station and adjacent Park Service residential area. Mud cracks and ripple marks are common. The formation is prominent on the side of Singleshot Mountain near the St. Mary entrance to the park, and everywhere immediately overlying the lighter-hued Altyn along the east edge of the Lewis Range where, especially when seen from a distance, it appears to have a purplish color. It also outcrops along the western base of the Livingstone Range (Figure 3D), but such exposures are as a rule obscured by a cover of dense forest. Accessible outcrops can readily be examined along Going-to-the-Sun Highway for several miles east of Sun Point and near McDonald Falls, and also along the lower part of the Grinnell Glacier trail.
GRINNELL FORMATION. Because of their dominantly red color, the shaly argillites which comprise the bulk of this formation are the most conspicuous rocks in the park. They lie immediately on top of the Appekunny and although their thickness varies considerably it is greater than 3,000 feet in several localities. Interbedded with the red argillites are thin white layers of quartzite, a former sandstone which has been converted by pressure into an extraordinarily hard, dense rock. Mud cracks, ripple and current marks, raindrop impressions, and other features made while the sediments were accumulating are common. The red color is due to abundant iron oxide occurring mainly as a cement between the sand and mud grains. All the rocks of Glacier Park contain some iron, or rather contain iron-bearing minerals. These minerals have various colors unless they have been oxidized, in which case the color is red or brown. Oxidation of the Grinnell formation probably took place while the mud was accumulating and during those periods when it was exposed to the atmosphere. At such times also the mud dried and cracked, the marks of which are so prominent on the surfaces of the layers today.
The Grinnell formation seems to be everywhere. In the Many Glacier region it comprises the bulk of Grinnell Point, Altyn Peak, and Mount Allen, and is no less striking in the bases of Mount Wilbur and the Garden Wall. Ptarmigan Tunnel is drilled through it, and the trails to Grinnell Glacier, Cracker and Iceberg Lakes cross it. Redrock Falls, on the trail to Swiftcurrent Pass, and Ptarmigan Falls on the Iceberg Lake trail drop over several of its highly colored layers.
From the Blackfeet Highway on top of Two Medicine Ridge one can see the dark red rocks of this formation capping the summits of Rising Wolf and Red Mountains. Even from the valley floor it is just as noticeable. Sinopah Mountain standing alone and impressive across the lake from Two Medicine Chalets carries the red banner of the Grinnell formation.
These red rocks constitute an important scenic feature for many miles along Going-to-the-Sun Highway. If one begins his trip on this highway at its east entrance he soon finds himself in the midst of a group of imposing red peaksGoat and Going-to-the-Sun on the right, Red Eagle and Mahtotopa on the left. The road crosses the formation along a mile and a half stretch just west of Baring Creek bridge. Innumerable loose slabs of red rock along the side of the road contain excellent mud cracks and ripple marks. Near Avalanche Creek on the west side of Logan Pass the highway crosses the Grinnell where it comes to the surface on the western limb of the big syncline.
The formation is well exposed in the vicinity of Sperry Chalet and Glacier. It forms all the mountains surrounding the basin in which the chalet is located, and the trail from chalet to glacier lies wholly on it. At the glacier intensely folded white quartzite layers and red argillites are very conspicuous.
The visitor can readily trace the Grinnell from place to place throughout the entire park area, and can thus easily visualize that it as well as all other formations at one time filled the intervening spaces between the mountains. (See color of cover pages.)
SIYEH FORMATION. Next above the Grinnell is a thick limestone formation which, because of its weathered buff color, stands out in sharp contrast to the red beds upon which it rests. It is the greatest cliff-maker in the park and in several places its entire thickness of 4,000 feet may be exposed in a single nearly vertical cliff. Since it is younger than the three preceding formations, it is confined mainly to the higher elevations, capping many of the loftiest peaks within the Lewis and Livingstone Ranges. In the Many Glacier area such peaks are Mount Gould and the Garden Wall, Mounts Siyeh, Grinnell, Allen, Wilbur, and Henkel. A number of others including Little Chief, Jackson, Gunsight, Fusillade, Going-to-the-Sun, Piegan, Pollock, Cannon, and Heavens Peak, are visible from Going-to-the-Sun Highway. The huge peaks Kinnerly, Kintla, Carter, and Rainbow which stand guard at the heads of Kintla and Bowman Lakes are composed of the Siyeh. The list also includes Cleveland, highest and largest of all.
Within the Siyeh there is a bed, averaging about 60 feet thick, composed almost entirely of fossil algae which apparently formed an extensive reef or biostrome on the floor of the shallow Belt Sea. The algae colonies are in the form of rounded masses up to several feet in diameter and bear a crude resemblance externally and internally to a head of lettuce or cabbage. Geologists know these algae by the genus name Collenia. Because of the rounded and smoothed surfaces on these colonies, mountain climbers frequently find the reef difficult to cross. It appears as a distinct light gray horizontal band on the east face of Mount Wilbur about midway between the base of the cliff and the peak's summit, where it can easily be seen from Many Glacier Hotel and Swiftcurrent Camp. It is also discernible on the Pinnacle Wall above Iceberg Lake and in Mount Grinnell. The Swiftcurrent Pass trail crosses it just east of the pass, and it is also exposed along Going-to-the-Sun Highway below the big switchback on the west side of Logan Pass where attention is directed to it by a sign. Unweathered portions of the reef rock are light blue. A similar but thinner reef outcrops at Logan Pass near the start of the Hidden Lake trail. Although most of the fossil algae occur in the Siyeh they are present in the younger formations and also in the Altyn. Other than algae the only undoubted fossils of the Belt series within Glacier National Park are burrows probably made by worms. They are rare and are restricted mainly to the Siyeh formation.
At the top of the Siyeh are several hundred feet of sandy and shaly beds, mostly reddish in color, grouped by some geologists into a distinct formation known as the Spokane. At Logan Pass it is about 700 feet thick and is well exposed in the lower parts of Clements and Reynolds Mountains, and at the site of the former "Clements" Glacier.
SHEPARD FORMATION. Several hundred feet of limy beds which weather yellow-brown lie on top of the Siyeh. Although named for outcrops on the cliff above Shepard Glacier (south of Stoney Indian Pass and near the site of the old Fifty-Mountain tent camp) the formation is exposed on the summit of Swiftcurrent Mountain at the head of Swift current Valley, on Reynolds and Clements Mountains near Logan Pass, and on Citadel and Almost-a-Dog, visible from Going-to-the-Sun Highway in St. Mary Valley. The formation is replete with mud cracks and ripple marks. Some rock surfaces exhibit two or three sets of the latter.
KINTLA FORMATION. These beds have the same bright red color as those of the Grinnell. However, because they are the youngest rocks of the Belt series they outcrop only on a few mountaintops, and inasmuch as these are mainly in the northwest part of the park, comparatively few people have noticed this formation. Visitors to Cameron Lake in Waterton Lakes National Park can see it in the red north wall of Mount Custer. The mountains around colorful Boulder Pass and Hole-in-the-Wall Basin are likewise composed of it.
Within the rocks of this formation there is a great abundance of small cubes believed to be casts of salt crystals which formed when the sediments were accumulating. Their presence indicates an arid climate and intensive evaporation of the sea, similar to the condition at Great Salt Lake today.
Last Updated: 11-Jul-2008