THE BUILDING OF THE COAST MOUNTAINS OF ALASKA (Historic Information)
A chain or system of mountains extends from Cape Horn to Attu. the longest on the globe, and perhaps the newest.
Its eastern slopes are more gentle, the western descends precipitously into the Pacific Ocean or rather at one time arose abruptly out of it.
Of Alaska the early explorers and geographers for many years made maps showing a continuous chain parallel with the coast, and so it appears to one at a distance on the sea; nevertheless it is bioken up in groups known in Southeastern Alaska as the Cascades, St. Elias, Wrangell, Chugach, and Kenai Ranges, and in Western Alaska as Aleutian Range.
Recent lava flows and volcanic action is first noticeable near Dixon Entrance, then at Sitka, where Mt. Edgecombe was active for about a half century after discovery by the Russians. But the smoking craters now begin near Cooks Inlet, and of the 150 volcanic cones an average of ten arc active. Shishaldin near Unimak Pass, being the most prominent.
The Aleutian Islands are but mountain tops of a range still growing.
Each year new islands appear, volcanoes are created, and the continent encroaches a little more on the sea. But the crust is cooling fast, soon the last volcano will cease to belch fire and the day of creation will be at an end.
Bogslof Island is perhaps the most attractive of the new-born islands; its oldest peak shot out of the ocean in 1796 to a height of 800 feet; others have been created and some have disappeared since. In 1906 the revenue cutter Perry was near by when a new island, now known as Perry Island, was created, and a year ago still another appeared, at which time the revenue cutter McCullough was near. The officers of the latter, as soon as possible, climbed over the steaming cone and took photographs of it.
Although the sulphur fumes and steam are disagreeable, sea lions and birds are already making it their home, and the Government during the last days of Roosevelt's park-making administration made it a bird reserve.
The red peaks, bare of vegetation, are common, and the dark red ash is everywhere apparent. The account given by the Harriman expedition is very explicit, and another is expected any time from scientific reconnoissance made made west of Unimak last year.
The Coast Range and Rocky Mountains seem to terminate in a grand climax of peaks above Cooks Inlet, or unite in the Aleutian Range, which is more and more submerged until only the very highest appear nearly at the shores of Japan. Whichever the fact may be, it is very evident that the Aleutian Mountains are hundreds of years younger and of a decidedly different formation.
The Coast Range from Mexico to Cooks Inlet consists generally of three kinds of material, erected in as many distinct epochs.
First. Following the Silurian and Devonian ages, sediments settled, solidified and hardened, becoming flexible sandstone, limestone and the like. These water-made, stratified material form the foundation and lower one-fourth of the range. These old rocks are often found doubled, faulted, buckled and twisted, from which it is concluded that the first step in building these mountains must have been in the pliable age, when a great fold was raised in the earth's crust where the range now stands. The latter periods of these rocks bear fossils and signs of living creatures; the older ones do not. They did not seem to be mineralized, but in later periods seams and pores were sometimes filled with minerals by intense internal heats, the action of gases, water or eruptions.
Second. After the fold had become hardened, and perhaps after many coal beds had been formed (as they are found pitched up edgewise like the sand and limestone), it was opened, and through a crack the length of the range, from the interior was forced, not a sedimentary, but a fire-made (igneous) rock, much of which is classified or known to the miner and geologist as the "Greenstones." They are highly mineralized, and the period was the most mineral-producing of any, and in this second belt or period the miner expects to make his "strike." It occupies the second one-fourth of the bulk of the mountains.
Third. At a much later period, and again by internal force, the range was opeend up and the great diorite granitic cone or center piled high upon the others, sealing it (excepting volcanoes) forever. This igneous rock composes about half the material of the range, contains little mineral and forms a hard cap almost irresistible to the elements. This upheaval at least opened up the seams, exposed the mineral to the elements, and forced it into the softer and more porous rocks, where frost, rain. snow, glacier river, and at last man can get it.
If we compare the mountains to a book, then each age will be a leaf, and when turned back we plainly read in unmistakable records of stone, the creation and evolution of every creature, from the beginning of land and sea. animal and vegetable; also of the minerals, upheavals and construction of the continent.
We cannot fully open the pages, but the rams, snows, glaciers, frosts, rivers and miners have hewn deeply, and the eruptions have broken the lids and revealed records made thousands of years before the date set as the date of creation.
Chapter one "In the beginning the earth was without form and void," chapter two and three and so on, until the sediments began to settle, and then other chapters while they became resisting crusts, pushed up out of the water, carrying coral, sea grass, shells, and the lowest forms of sea life, etc.
Land and water being separated, the warm muds and slimes began to develop crawling reptiles; as they pushed up higher vegetation began to grow, and walking animals developed to eat it.
Before this range was formed, the storms, and upheavals gathered the slimes and tropical vegetation into the sags, then covered them over, preserving the coal and oil for our use, and the records and pictures for our enlightenment.
The general forms of the prehistoric forests of Alaska were similar to our ferns and evergreens, but on a larger scale. Could it be possible that the present dense woods date back to a parent so old?
These mountains present to the student and intelligent miner volumes of information on their upturned stratas.
The growth, or ageing of the range is no less interesting. Just as the wood of the tree or bones of the man grow dryer, harder and mature, then age and decay, so the rocks become metamorphosed, shistose and shaley.
The sediments of one age become the limestone of the next and marble of the next; the sands of the river and sea become sandstone, and the volcanic or eruptive intrusives become granite.
Five thousand years ago the present deserts of Africa, India, and China were the centers of the most advanced human habitations and covered with fertile fields of grain; they have died with the age.
How many ages we have had, we hardly know, but here in Alaska the sedimentary age, the age of greenstones, and of the diorite, are plainly shown; the coal age, the period of plant life, of reptiles, and of mastodons, and the glacial period are as unmistakably disclosed.
This is the age that yields to drouth, crystallization and fire; the age before it yielded to the ice cap and the floods.