Part 2

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 peaks--Goat 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 Swiftcurrent 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 and 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.

Igneous Rocks of the Belt Series

Not all of Glacier Park's rocks accumulated slowly and quietly as sediment in a body of water. At many places, interbedded with and cutting across the sediments, there are bodies of igneous rock which reached their present position in the form of hot molten material forced up from deep within the crust.

PROTEROZOIC

KINTLA 860'+ Red argillite SHEPARD 600' Buff limestone PURCELL 250' Black lava SIYEH 4000' Dark diorite bordered by white altered limestone Blue limestone. Weathers buff GRINNELL 1600-3000' Red argillite and white quartzite APPEKUNNY 2500'± Green argillite. Some white quartzite ALTYN 2300'± Gray limestone. Weathers buff

PURCELL LAVA.

Soon after the youngest layers of Siyeh limestone had accumulated on the floor of the sea and while they were still under water, a mass of molten rock was squeezed up from far below and extruded in the form of a submarine lava flow over the recently accumulated sediments. Several times this lava poured out forming a total thickness varying between 50 and 275 feet. One of the best exposures is on the west side of Swiftcurrent Pass and in Granite Park just west and northwest of the chalet. In fact it is this lava flow which gives the name, albeit wrongly, to Granite Park. The material of the flow is very fine-grained and dark (basic), in contrast to the light color and coarse grain of granite. Nonetheless, many prospectors are wont to call every igneous rock, regardless of its composition, a granite. A number of ellipsoidal structures ("pillows") up to two feet in diameter within this lava indicate that it was extruded under water. The Purcell is thickest in the vicinity of Boulder Pass, where the trail traverses its ropy and stringy surface for a distance of several hundred yards.

Later, after the Shepard and part of the Kintla formation were laid down on top of the Purcell, another similar flow spread over the sea floor.

DIORITE SILL.

Few persons visit the park without noticing the pronounced black layer, within the Siyeh formation, present on many of the high peaks. It is most in evidence on the face of the Garden Wall viewed from the vicinity of Many Glacier Hotel, although it is plainly visible also in Mount Wilbur and the wall above Iceberg Lake. Passengers on the Waterton Lake launch can see it cutting across the stupendous north face of Mount Cleveland. From Going-to-the-Sun Highway it can be seen on Mahtotopa, Little Chief, Citadel, Piegan, and Going-to-the-Sun Mountains, and on the west side of the Garden Wall, where it also forms the cap of Haystack Butte. It is everywhere about 100 feet thick, and thus can be used as a very accurate scale for determining the height of mountains on which it is discernible.

This imposing layer of rock, unlike the lava, never reached the surface in a molten state, but was intruded between beds of sedimentary rock and thus became a sill instead of a flow. We need only a glance to determine its intrusive nature. Wherever it occurs it is bordered at top and bottom by thinner gray layers. These are Siyeh limestone which was changed to marble by the tremendous heat of the diorite during its intrusion. This effect is termed contact metamorphism by geologists. Because this contact-metamorphosed zone is at both top and bottom of the sill we know the latter was intruded into the adjacent rocks. Lava flows, even though covered later by sediments, of course alter only the underlying rocks.

The sill can readily be examined in a number of places where trails cross it, notably at Swiftcurrent and Piegan Passes, and north of Granite Park near Ahern Pass. But nowhere is it as accessible as on Logan Pass. It lies beneath the parking lot at a depth of only a few feet, and is exposed on both sides of the pass. To inspect it, one need walk only about 200 yards along the trail leading to Granite Park. In a distance of less than 100 feet the trail traverses from fresh Siyeh limestone across the entire altered (contact-metamorphosed) zone, here 12 to 20 feet wide, into the center of the sill. All parts of the sill and adjacent rocks can readily be examined and studied in detail at this site.

A number of dikes of Belt age, some of which undoubtedly were feeders to the sill and flows, cut vertically up through the sedimentary formations. Some of the dikes are less resistant to weathering and erosion than the rocks surrounding them; consequently their more rapid removal results in the formation of narrow vertical chimneys or recesses which appear as snow-filled chutes on the mountainsides in spring and early summer. Such a feature almost invariably indicates the presence of a dike. From Many Glacier Hotel one of these can be seen on the red mountain in front of Mount Wilbur. Another, 1,500 feet high, transects the Pinnacle Wall at the outlet of Iceberg Lake. The dike which forms this impressive chute is less than thirty feet wide. Though not so conspicuous as the sills some of these dikes are of interest because they contain various ore minerals, principally copper, which today form small deposits along their borders. About the beginning of the century these were responsible for a short-lived mining boom, the best known vestige of which is the remains of the mill at Cracker Lake. The old Cracker Mine, with entrance now caved in, was driven along a dike which has a width of over 100 feet.

From the boat landing at the head of Josephine Lake the dump of another mine appears as a tiny gray-green mound on a narrow shelf high on the precipitous wall of Grinnell Point. Like the Cracker Mine this one was dug along the edge of a similar but smaller dike. All these deposits are insignificant in size and of no commercial value. Had they been important this great area might never have been set aside as a national park.