IN STARRY SKIES

Evening Post, Volume CXVII, Issue 111, 12 May 1934, Page 22

IN STARRY SKIES

METEOR CRATER ARIZONA

(By "Omega Centauri.")

Most of the astronomers who are opposed to meteoric theory of tho originl of the lunar craters rely chiefly on-tho single argument that, if meteors produced the mighty rings that cover the greater .part of. the visible, hemisphereof the moon,, the earth must have been. subjected to a bombardment at least equally intense. Where, they ask, are the terrestrial scars? This

argument is not of such weight as is nsually supposed. Many of the most characteristic features of the lunar scenery seem to date from a time when the solid crust was comparatively thin. 2s Tow the earth, with a mass more than SI times that of the moon, must have taken very much longer to cool. Tho great harvest of meteoric matter, provided by the encounter which gave birth to the solar system, must have been gathered in by the sun, tho planets, and their satellites at a time when all the larger bodies were entirely in'the*liquid or the gaseous state. The larger bodies wcro thus unablo to retain any permanent impression of the bombardment. Even after the earth acquired a sblid crust conditions on its surface "were entirely different from those on the moon. The earth's atmosphere is sufficiently dense to vaporise small meteors and reduce to a fraction the speed of all larger ones. Then denudation continually remodels the surface and obliterates old scars. But in spite of this many astronomers 'felt that if the meteoric theory were true we should be able to find some similar forms on earth. For this reason the discovery aud interpretation of Meteor Crater is of groat historical importance. The Hopi Indians have a tradition that one of their gods descended from the sky in clouds of fire to bury himself there. But when Coon Mountain or Coon Butte, as it was called, was found, by white'men they took.it for granted that it was a volcano. Many papers have bec:u-,\vritton about.it since 1891. G. K. Gilbert in 1895 first suggested its meteoric origin; But most of the work that has led to the confirmation of this theory is due' toJIr.'D. M. Barringer, a geologist and mining engineer.

The crater lies close to the old Santa ITe Trail, which has now been superseded by the A.T. and S.F. Railway, and Sunshine station on that line is sis miles due north, of it. It is surrounded by what is almbst a desert plain, broken

within three miles. by tho famous Canyon Diablo. .Irrigation works are now changing the character of parts of Arizona, but large tracts still remain in their natural state. Vegetation is scanty and stunted,.and in many places even the soil has been blown" away, leaving the rod or purple sandstone exposed. The district has thus earned the name of the Painted Desert. - Tho rocks are those of tho Grand Canyon scries, and around Meteor Crater aro horizontally stratified. First there are 40 or 50 feet of purplish red shaly sandstone, under this 250 to 300 feet of yellowish grey arenaceous limestone, then 1000 ft of white or grey saccharoidal sandstone, and under this dark red sandstone.1 This last layer has been found by drilling to bo unaltered, and lying in a horizontal position, underneath the crater. This fact alone seems to givo conclusive evidence against the volcanic theory. Moreover no igneous rock of any kind has been found within nine miles of the crater. Seen from a distance, Meteor Crater looks like, a low fiat-topped hill, and appears very much the*'same from whatever direction it is viewed. When, however! you climb on to the circular rim, which is about 130 feet above the i desert plain, you look into a hollow 570 feet deep, the present floor being about 440 feet below the level of tho outer plain. The inner walls, in most places, are very steep, artd the strata have I been tilted so that they dip away from the centre. The cavity is a little more than three-quarters of a mile in diameter. For ha]f a raile along . the southern rim the limestone and underlying sandstone have been raised 105 ft. Mr. Barringer estimates the weight of tho portion lifted to be between 20,000,000 and 30,000,000 tons. The elevated ring is composed of rock fragments of all sizes and shapes, from blocks of limestone weighing 4000 tons or more down to microscopic particles of crystalline quartz. Probably 15 or 20 per cent, of tho total mass ejected, estimated.'to exceed.3oo,ooo,ooo tons, consists of these " minute .fragments .in "the.form.known as silica or rock flour. Nearly'all.'of it' will pass through the finest wire screen 200 meshes to the inch. This rock flour, mixed with,rock fragments,, great and small, forms the floor of the crater. The drills did not reach undisturbed rock until they penetrated to\two iorthree times the depth of the present crater floor. In fourteen eases meteoric material was found at depths:ranging from 450 to1 6So,fcet: Meteoric material is also- found seat' tered all round the crater, but. never more than 5* milos from, its rim. It [increases in, abundance as ; oii© draws near to,the crater. Many thousands oi! specimens have been collected. It is said that the number found near Coon Butte is greater than,from all jfcho rest of the world. These meteorites are spread over a much larger circle than the fragments of rock. Thp latter, often* weighing from

50 to several hundred pounds, arc found only within two miles of the crater.

Wo owe our knowledge of this most 'interesting spot chiefly, us we have said, to Mr. D. M. Barringer. As soon as he heard that pieces of meteoric iron had been found near it he realised that in all probability the cavity was due to a meteorite or meteoric s\varm. Establishing a camp on the rim", he made a, thorough .examination of the crater and its surroundings. The first borings wore made near the con Ire of the hollow, the circular form having suggested that the meteorite fell nearly vertically. But for some eight hundred feet they came only to rock fragments and rock flour. It is now believed that what Temains of the swarm is under the £*ithern wall, where tho strata were lifted 100 feet. ,In a boring made there the drill at a depth of 137G feet lodged in something extremely hard, and it was determined to try to reach it by sinking a shaft outside the disturbed area. , Mr. Barringor originally I estimated the probable ' mass of the meteorite at some 10,000,000 tons. But according: to the meteoric explosion theory it need not have been nearly so massive. But the. important point is that, here at last was.found on earth a structure closely resembling tho typical lunar ring, arid that after, careful investigation'it isldennitely acknowledged to be of meteoric origin. This great discovery did.not for very long stand alone. Somewhat similar forms have been discovered in various parts ,of the globe. We hear, for instance, of thirteen craters, varying in size from 220 to 10 yards across, being found at Henbury in Central Australia, scattered over an area half a mile square. The largest of tfieso is 50 feet deep, and 800 meteorites, ranging from 501b to a few ounces in weight, were found strewn around, whilst sandstone rocks in the vicinity, had been melted. Then in Alaska, what is described as a. "Moon Crater,?''seven miles in diameter, was seen from Elephant Mountain near Aniakch'ak. Another crater due to a meteorite was discovered in tho Pamir in Central Asia. Then in Carolina, j scattered over an area of 40,000 miles,) are' more than 1500 oval depressions, the largest, ones being between one and two miles in diameter. Judging from the shape of'the area struck it is estimated that, if the swarm of meteorites was globular, four-fifths must have fallen in the Atlantic Ocean and on the Appalachian Mountains. Other instances could be given, and owing to the development .of aviation probably many inoro: discoveries will be made in the near future. Mr. Barringer was led by his study., of 'Meteor Crater to think of. the craters of the moon, and in a paper published in 11914' he oxpreses his belief that they are of meteoric origin. In a later pamphlet, which unfortunately is not dated, he gives "A discussion' of-the Origin of the Craters .and.other Features of the Lunar Surface.',' ' '