Mexico and forms the northern flank of the southern or Arizona 

 mountain block. This massif is arid though clothed all over its 

 upper reaches with either open or closed coniferous forests of 

 pines and junipers. It contains many upland plateaus, and large 

 parts of it are still true wilderness. If we descend from its 

 northern rim onto the central plateau and start up the course of 

 the Puercos River, we may turn aside to visit another remarkable 

 natural phenomenon. This is the largest and most readily acces- 

 sible meteorite crater in the United States and one of the most 

 prominent and most recently formed in the world. 



It is an enormous bowl-shaped hole, 4150 feet across, three 

 miles around the rim, and 570 feet deep, sunk in the middle of 

 a slight rise on a more or less level plain. It was not recognized 

 as being of meteoric origin until almost sixty years after its 

 discovery in 1871, but it was the first crater on earth to be so 

 recognized. Since then, similar phenomena have been discovered, 

 or reappraised for what they really are, in increasing numbers 

 all over the world. Most active in this novel exploration recently 

 have been the Canadians who, stimulated by the discovery of 

 the enormous Chubb Crater in the Ungava Peninsula (see 

 Chapter 2) from the air in 1948, worked over their aerial surveys 

 and found a dozen more. Some of these are so ancient that they 

 are completely filled in and can at first be recognized only by 

 their distinctive shape and the fact that different types of vegeta- 

 tion grow around their rims, whereas others are filled with lakes 

 that form parts of circular depressions. Later borings and other 

 investigations have confirmed their nature. 



The debate about these phenomena, since they have been 

 accepted as such, has centered around the method of their forma- 

 tion. At first it was believed that a large meteorite too big to 

 burn up in passing through the atmosphere, crashed into the 

 ground with such force as to smash its way into the rocks 

 until it came to rest, like a bullet ploughing into a tree trunk. 

 An immense amount of time, money, and labor was spent in 

 probing for buried meteors in the hope of being able to mine 

 them, as they are usually composed of almost pure nickel-iron. 

 No such great metallic mass has even been located, let alone 

 excavated from under any of these big craters. The next theory 

 was that the craters were formed by swarms of little meteors 

 that bombarded a single point on the earth in a stream, breaking 

 up the rock surface and scattering to form crater-like cones, just 

 as you may do by shooting a shotgun shell at sand. At first there 

 seemed to be considerable confirmation of this idea, for, although 

 no whole meteorites were located under craters, a lot of meteoric 

 iron has been detected both in and around many of them. In 

 this Arizona crater — the Barringer, as it is now named — a large 

 amount of such iron has been located by gravimetric methods 

 about a thousand feet below the south rim, and much more is 

 scattered widely all about, the total calculated to aggregate some 

 three million tons. This would form a sphere about five hundred 

 feet in diameter. I may add that this iron would be valued at 

 about a hundred dollars per ton today. 



Recently, however, it has been pointed out that a meteorite 

 of this size, hitting the earth at a terrific speed, amounts almost 

 to the proverbial irresistible force meeting an immovable object; 

 and that, on approaching that impossible situation, a number of 

 strange things happen. At the exact moment of impact of the 

 leading edge of the meteorite with the surface of the earth's rock 

 crust, the meteorite is indeed virtually an irresistible object; 

 while the earth, being the greater mass, is an immovable one. 

 The latter therefore absorbs the shock and stops the movement 

 of the meteor, but this occurrence releases a fantastic amount of 

 pent-up energy that has to be absorbed or disseminated. This is 

 mostly in the form of heat, but heat so great and so suddenly 



produced that it becomes explosive — molecularly and in extreme 

 cases even atomically— so that electrons are actually blasted 

 from their orbits. {This has been done under experimental condi- 

 tions by pressure alone.) However, during the split second before 

 this condition is created in the meteorite, that body has pene- 

 trated some distance into the rock surface of the earth, both 

 shattering it and subjecting it to unimagined pressures. As it 

 comes to a stop, the meteorite blows up like a monumental 

 bomb, its energy of movement or momentum having all been 

 converted into heat; and it "goes off" in all directions, not only 

 downward. This, aided by the spring-back of the rocks, results in 

 a minor "volcano" on the surface — which causes the crater and 

 explains the masses of shattered rock and the bits of meteoriiic 

 iron that are found scattered for miles around. It also explains 

 why there is no single solid meteoric body below. 



It is now believed that in some cases the entire meteorite may 

 be thus volatilized, leaving practically no solid residue. In 1908 

 one estimated to have weighed more than a million tons struck 

 in Siberia. This appears to have been a multiple meteor or a 

 shower; for, although all of it was apparently volatilized, ten 

 large craters, the biggest 165 feet in diameter, and a host of 

 smaller ones were formed. It landed in daylight, but it was seen 

 hundreds of miles away and its heat was felt for fifty miles. Four 

 hundred miles away it rocked a railroad engine to a stop, and 

 all trees in the dense taiga forest where it landed were knocked 

 down for forty miles all around. 



The Barringer Crater today is an austere thing to look at. It is 

 without any natural beauty or charm, and it gives one the 

 impression of being just what it is: a vast shell hole or bomb 

 crater. It obviously did not grow on this old earth, and it seems 

 somehow to be a rude imposition. 



A FOREST OF OPAL 



Sixty miles east of this crater there is still another fascinating 

 sight. This is a vast petrified forest. These phenomena are found 

 all over the world and there are many on this continent, but this 

 is a most spectacular example and perhaps the most instructive. 

 These trees are incredibly ancient, having been dumped into 

 saturated ground or into the silt at the bottoms of rivers or lakes 

 when they were waterlogged in what the geologists call the 

 Triassic Period, some two hundred million years ago. These 

 deposits are today called the Chinle beds and are in some places 

 three hundred feet in ihickness. The individual layers often 

 show, on their surfaces, mud cracks such as one sees around 

 drying lakes today, ripple marks, and even giant rain spots. The 

 theory is that these trees grew elsewhere and were washed down 

 in freshets and dumped into shallow lakes. Although this is 

 possible, it seems improbable, since many of them have con- 

 siderable portions of quite slender roots and branches still in 

 place and undamaged, and almost all of them still have their 

 bark complete and perfectly preserved. What is more, many are 

 really very big trees, and it would take more than a mere freshec 

 to float them without scouring them completely. It seems much 

 more likely that they grew in situ and were blown down from 

 time to time by hurricanes, as the great trees of today sometimes 

 are, and fell into a nearby river and then sank, just as today the 

 great cypresses do into such rivers as the Suwannee in Florida 



The South Montane Province has almost every variety of 

 growth — even massed forests of Quaking Aspen on its 

 higher mountain slopes. 



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