The Book of the National Parks

by Robert Sterling Yard

III

But, with Glacier, this is not enough. To see, to realize in full its beauty, still leaves one puzzled. One of the peculiarities of the landscape, due perhaps to its differences, is its insistence upon explanation. How came this prehistoric plain so etched with cirques and valleys as to leave standing only worm-like crests, knife-edged walls, amphitheatres, and isolated peaks? The answer is the story of a romantic episode in the absorbing history of America's making.

Somewhere between forty and six hundred million years ago, according to the degree of conservatism controlling the geologist who does the calculating, these lofty mountains were deposited in the shape of muddy sediments on the bottom of shallow fresh-water lakes, whose waves left many ripple marks upon the soft muds of its shores, fragments of which, hardened now to shale, are frequently found by tourists. So ancient was the period that these deposits lay next above the primal Archean rocks, and marked, therefore, almost the beginning of accepted geological history. Life was then so nearly at its beginnings that the forms which Walcott found in the Siyeh limestone were not at first fully accepted as organic.

Thereafter, during a time so long that none may even estimate it, certainly for many millions of years, the history of the region leaves traces of no extraordinary change. It sank possibly thousands of feet beneath the fresh waters tributary to the sea which once swept from the Gulf of Mexico to the Arctic, and accumulated there sediments which to-day are scenic limestones and shales, and doubtless other sediments above these which have wholly passed away. It may have alternated above and below water-level many times, as our southwest has done. Eventually, under earth-pressures concerning whose cause many theories have lived and died, it rose to remain until our times.

Then, millions of years ago, but still recently as compared with the whole vast lapse we are considering, came the changes which seem dramatic to us as we look back upon them accomplished; but which came to pass so slowly that no man, had man then lived, could have noticed a single step of progress in the course of a long life. Under earth-pressures the skin buckled and the Rocky Mountains rose. At some stage of this process the range cracked along its crest from what is now Marias Pass to a point just over the Canadian border, and, a couple of hundred miles farther north, from the neighborhood of Banff to the northern end of the Canadian Rockies.

Then the great overthrust followed. Side-pressures of inconceivable power forced upward the western edge of this crack, including the entire crust from the Algonkian strata up, and thrust it over the eastern edge. During the overthrusting, which may have taken a million years, and during the millions of years since, the frosts have chiselled open and the rains have washed away all the overthrust strata, the accumulations of the geological ages from Algonkian times down, except only that one bottom layer. This alone remained for the three ice invasions of the Glacial Age to carve into the extraordinary area which is called to-day the Glacier National Park.

The Lewis Overthrust, so called because it happened to the Lewis Range, is ten to fifteen miles wide. The eastern boundary of the park roughly defines its limit of progress. Its signs are plain to the eye taught to perceive them. The yellow mountains on the eastern edge near the gateway to Lake McDermott lie on top of the Blackfeet Indian Reservation, whose surface is many millions of years younger and quite different in coloring. Similarly, Chief Mountain, at the entrance of the Belly River Valley, owes much of its remarkable distinction to the incompatibility of its form and color with the prairie upon which it lies but out of which it seems to burst. The bottom of McDermott Falls at Many Glacier Hotel is plainly a younger rock than the colored Algonkian limestones which form its brink.

Perhaps thousands of years after the overthrust was accomplished another tremendous faulting still further modified the landscape of to-day. The overthrust edge cracked lengthwise, this time west of the continental divide all the way from the Canadian line southward nearly to Marias Pass. The edge of the strata west of this crack sank perhaps many thousands of feet, leaving great precipices on the west side of the divide similar to those on the east side. There was this great difference, however, in what followed: the elongated gulf or ditch thus formed became filled with the deposits of later geologic periods.

This whole process, which also was very slow in movement, is important in explaining the conformation and scenic peculiarities of the west side of the park, which, as the tourist sees it to-day, is remarkably different from those of the east side. Here, the great limestone ranges, glaciered, cirqued, and precipiced as on the east side, suddenly give place to broad, undulating plains which constitute practically the whole of the great west side from the base of the mountains on the east to the valley of the Flathead which forms the park's western boundary. These plains are grown thickly with splendid forests. Cross ranges, largely glacier-built, stretch west from the high mountains, subsiding rapidly; and between these ranges lie long winding lakes, forest-grown to their edges, which carry the western drainage of the continental divide through outlet streams into the Flathead.

The inconceivable lapse of time covered in these titanic operations of Nature and their excessive slowness of progress rob them of much of their dramatic quality. Perhaps an inch of distance was an extraordinary advance for the Lewis Overthrust to make in any ordinary year, and doubtless there were lapses of centuries when no measurable advance was made. Yet sometimes sudden settlings, accompanied by more or less extended earthquakes, must have visibly altered local landscapes.