49^ 



NA TURE 



[September 13, 1900 



The fragmental material of the rim consists of 

 I he debris of the strata in which the crater has been 

 formed, tlie bloclis being piled one upon another in 

 ihe utmost confusion. Further, there are many 

 millions of tons of pulverised sand-grains, much of 

 the material being an impalpable powder. It con- 

 stitutes a great part, not only of the rim, which is 

 three miles in length round the base, but also of 

 the bottom of the crater, for it has been found by 

 means of bore-holes to e.Mend to a depth of more 

 than 850 feet. 



The masses of meteoric iron, being of pecuniary 

 value as specimens, have been much sought for, and 

 masses small and large, amounting altogether to 

 about fifteen tons, have been found among the upper 

 blocks on the rim, and on or near the surface of 

 fhe surrounding plain in all directions from the 

 craler; none have been found within the latter. 

 Several masses weigh from 600 lb. to more than 

 1000 lb. Mr. Gilbert states that some of the iron has 

 been found outside the range of the rock debris, one 

 large mass being as much as eight miles distant from 

 the crater. There have also been found lumps of 

 o.xide of iron, in great quantity and having a similar 

 distribution to that of the metal. Mr. Gilbert (and 

 also Dr. Foote) regarded them as also being of 

 meteoric origin, and as perhaps having resulted from 

 the weathering of a particular constituent of the 

 meteorite, namely, the protosulphide of iron ; but Mr. 

 Barringer and Mr. Tilghman have found that they 

 contain much nickel, and that many of them consist 

 internally of magnetic oxide of iron, sometimes itself 

 containing a nucleus of meteoric iron. Mr. Barringer, 

 like Dr. Foote, suggests that the magnetic oxide 

 resulted from the combustion of the iron when the 

 meteorite was travelling through the air, but in the 

 opinion of the present writer all the oxide, mag- 

 netic or not, is a result of weathering. There has 

 been plenty of time for this action, for cedars now 

 700 years old are growing on the rim of the moun- 

 tain. Further, the masses of iron found on the surface 

 of the plain must have penetrated the earth to some 

 depth at the time of the fall, and have been since 

 exposed by denudation of the penetrated material. 

 The authors roughly estimate the fall to have taken 

 place not more than 5000 years ago, perhaps much 

 less. 



Though all the masses of iron found in the rim 

 have been got from the surface, lumps of the meteoric 

 oxide have been met with to a depth of 27 feet, 

 and this is of interest because some of them were 

 lying beneath big blocks of sandstone, through which, 

 whether as metal or as oxide, they could not have 

 passed. They must have taken up their present posi- 

 tions at the same time as the blocks themselves. To 

 the present writer it seems probable that thev had 

 been buried, possibly a long time, in the upper layers 

 of sandstone, and were ejected with the rock-frag- 

 ments when the crater was formed, but Mr. Barringer 

 explains them as fragments which had been broken 

 from the asteroid during its passage through the air, 

 had diverged from the path of the meteor, and had 

 while still burning become entangled, and afterwards 

 smothered, among the blocks of sandstone and minute 

 di'bris projected into the air through the penetration 

 of the earth by the main mass. 



.\s for the enormous amount of pulverised silica, 

 the authors hold that it cannot have been produced 

 otherwise than by the action of an enormous pro- 

 jectile penetrating the sandstone. But it is difficult 

 to see why the crushing of the grains could not 

 have been produced by an enormous pressure of 

 steam, such as must have preceded, according to 

 Mr. Johnson, the formation of the crater. The fol- 



NO. 1924, VOL. 74] 



lowing remark made by the late M. Daubr^e was 

 published by him in 1879, before Coon Mountain had 

 been heard of, and is also suggestive (" G^ologie Ex- 

 p^rimentale," part ii., p. 645): — "In the deep and 

 hot portions of the globe, for instance in volcanic 

 reservoirs, water is present under enormous pressure. 

 The pressure of that which forces lava up to the 

 summit of Mt. Etna must certainly exceed 1000 

 atmospheres. It is therefore quite comparable with 

 the tension developed in the chamber in which these 

 experiments have been made. When water escapes 

 to the surface by narrow fissures in such circum- 

 stances, it must bring different substances into a 

 state of pulverisation simulating that of volatilisa- 

 tion." 



Two other observations are relied on by the authors 

 in their support of the asteroidal hypothesis. Accord- 

 ing to the first observation, obstacles at a great depth 

 and probably of small size were found to interfere 

 with the boring. They were inferred, chieflv from 

 their hardness and from the difficulty of removal of 

 a magnet let down to the bottom of the bore-hole, 

 to be probably metallic iron, and to be parts of the 

 broken asteroid. But the presence of some small 

 masses of iron beneath the crater is to be expected if 

 all the masses were lying embedded in the sandstone 

 before the crater was formed. Those which were pro- 

 jected nearly vertically upwards must have fallen back 

 into the large hole and be deep down among the 

 debris. .'According to the second observation, a 

 stratum at a considerable depth contains small par- 

 ticles of oxide of iron thought to be of meteoric origin. 

 The same kind of material is said to occur on the 

 surface of the surrounding country for several miles. 

 The material in which these small particles of oxide 

 are distributed in the crater must either be in situ or 

 have fallen back into the hole : in the former case 

 they cannot be of meteoric origin, for small particles 

 would not have had the requisite penetrative power; 

 in the latter case, it is probable that they were lying 

 near the surface before the steam-explosion, and fell 

 back with the fragmental material into the hole. 



It is found as a matter of experience that meteorites 

 on striking the ground have a comparativelv small 

 velocity — only a few hundreds of feet a second. Is 

 it possible that an asteroid after passing through the 

 earth's atmosphere could retain a velocity large 

 enough for the production of such a crater? .Apply- 

 ing a method devised by .Schiaparelli and numerical 

 data obtained from artillery experiments, the present 

 writer has made some calculations as to the velocity 

 of a meteoritic ball on reaching the ground, the ball 

 being supposed to have a specific gravitv seven times 

 that of water, to have entered the earth's atmosphere 

 at a speed of fifty miles a second, and to have travelled 

 vertically. Neglecting the small additional velocity 

 due to the action of gravity for the few seconds of 

 flight, and the diminution of size of the ball during 

 the flight, the numbers are as follows : — 



Radius of ball Final velocily 



in metres in metres 



01 21 



lo 694 



100 2590 



1000 8261 



looo-o ... ... ... ... 25,461 



According to Mr. Gilbert, it has been found in 

 artillery experiments that a spherical projectile -fill- 

 ing solid limestone with a velocity of 1800 feet a 

 second will penetrate to a depth of something less 

 than two diameters. It would appear, then, that a 

 meteorite of large size would not be prevented bv 

 the earth's atmosphere from having a penetrative 

 effect sufficient for the production of such a crater. 



L. Fletcher. 



