September 13, 1906] 



NA TURE 



491 



diameler; for the next half-mile the fragments are 

 smaller and less plentiful; beyond this distance they 

 are isolated from each other, and become smaller and 

 less frequent as the distance from the crater increases. 



In 1886 some shepherds encamped on the slopes 

 of Coon Mountain found among the rock-fragments 

 on the rim some lumps of iron, which they mistook, 

 as is not infrequently the case, for native silver. 

 The general distribution of the fragments and the 

 nature of their material suggested to the shepherds 

 that all the scattered masses, both stony and metallic, 

 had been shot from the crater of the mountain. A 

 IfW years later some of the melal fell into the hands 

 ot the late Dr. .-V. E. Foote, of Philadelphia, for whom 

 It was analysed by Prof. G. A. Koenig, of that city. In 

 structure and chemical composition the metal proved 

 to be identical with ordinary meteoric iron, but of 

 e.xceptional interest as enclosing microscopic diamonds. 

 Since that time the celestial origin of the iron masses 

 found about Coon Mountain has been recognised as 

 beyond doubt, and the meteorite has become well 

 known imder the name of Canon Diablo, small masses 

 having been found in the canon of that name distant 

 about two and a half miles from the mountain. 

 During the oral discussion which followed the read- 

 ing of the paper of Dr. Foote on August 20, 189 1, 

 before the American Association for the Advancement 

 of Science, Mr. Gilbert, who chanced to be present, 

 suggested that the fall of the iron masses might have 

 been connected with the formation of the crater, and 

 that the large hole might have been caused by the 

 penetration of the earth by an enormous iron 

 meteorite, perhaps 1500 feet in diameter, large enough 

 to be termed an asteroid. In such case the asteroid 

 IS buried in or near the hole and probably at no 

 great depth. 



Not being at that time at liberty to visit Coon 

 Mountain himself, Mr. Gilbert asked his colleague, 

 Mr. Willard D. Johnson, to examine the district and 

 try to discover what had been the mode of origin of 

 the crater. On his return Mr. Johnson reported that 

 the crater had probably been produced by a tre- 

 mendous steam explosion, the fragmental material 

 around being the original contents of the hole. 

 Within a radius of fifty miles there are hundreds of 

 vents, from which lava has issued during the later 

 geological periods, and thus there existed at one time 

 a neighbouring mass of molten material sufficient 

 to account for the production of the required amount 

 of steam. In such case the fall of the masses of iron 

 had been independent of the formation of the crater. 



The rocks in the region containing the crater, how- 

 ever, are stratified and of sedimental origin, and the 

 strata, except at the hole itself, are still quite hori- 

 zontal. They are of late Carboniferous age, and con- 

 sist, to a considerable depth, of coloured sandstones, 

 one kind being so calcareous as to have claims to be 

 regarded as a limestone. But all round the hole 

 itself the strata have been bent, and are now directed 

 upwards, approximately towards the same point. 



This explanation and report being of an extraor- 

 dinary character, Mr. Gilbert's interest in the problem 

 became even greater than before, and he soon seized 

 an opportunity of making an examination himself. 

 This was done with such minuteness that he was 

 able to draw contour lines of the crater and district 

 for every ten feet of difference of level, and could 

 form an approxirnate estimate as to the positions 

 of tlie contour lines at the time the crater had been 

 formed ; hence he was able to calculate the respective 

 volumes of the crater and the fragmental material. 

 He came to the conclusion that the two volumes were 

 virtually equal (eighty-two millions of cubic yards), 

 and thus that no asteroid could have buried itself 



NO. 1924, VOL. 74] 



there. Further, he made a delicate magnetic survey 

 of the district; no magnetic disturbance being dis- 

 coverable, he concluded that no mass of iron large 

 enough to have produced the crater could be lying 

 within some miles of the earth's surface, whereupon 

 lie renounced the asteroidal hypothesis, and accepted 

 the explanation which had been given by his colleague. 



Some years later the crater and the speculations as 

 to its origin became known to Mr. D. M. Barringer 

 and Mr. B. C. Tilghman. ITiey formed the opinion 

 that the asteroidal hypothesis had been renounced by 

 Mr. Gilbert on insufhcient grounds. In the first place, 

 according to their calculations, there is a great differ- 

 ence between the volume of the crater and that of 

 the fragmental material; in the second place, the 

 absence of magnetic disturbance may be due to the 

 asteroid having been broken up into smaller masses, 

 each of them polarised, and each having its magnetic 

 axis in an accidental direction. So convinced were 

 they that in 1903 thev " located " the mountain under 

 the United States Mineral Land Laws, and at great 

 expense proceeded to sink shafts and make bore-holes 

 with the hope of finding the buried asteroid. The 

 results of this work, so far as it has ypt gone, were 

 recently recorded in two papers published in the 

 Proceedings of the Academy of Natural Sciences of 

 Philadelphia (December, 1905). One of them has- 

 been written from the point of view of the geologist 

 (Mr. Barringer), the other from those of the physicist, 

 chemist, and mathematician (Mr. Tilghman). Tlie 

 former says : — " They do not leave in my mind a 

 scintilla of doubt that this mountain and its crater 

 were produced by the impact of a huge meteorite 

 or small asteroid"; the latter feels that "he is 

 justified, under due reserve as to subsequently de- 

 veloped facts, in announcing that the formation at 

 this locality is due to the impact of a meteor of 

 enormous and unprecedented size." 



It may be mentioned that a few years ago a suc- 

 cessful search was made by Finnish geologists for 

 a large meteorite which was believed bv them to 

 have buried itself within a certain area. But in that 

 case the presumptive evidence was very strong. .A 

 meteor had lighted up a large extent of the country, 

 and the next morning a newly made hole, with cracks 

 radiating from it in various directions, had been 

 found in the ice covering the Baltic Sea. near Bjur- 

 bole, in Finland. After a patient search the mass 

 was at last located at a considerable depth below the 

 sea-bottom, and eventually extracted. What are the 

 prospects of a similar success at Coon Mountain? 



For many miles round the crater the order of suc- 

 cession of the rocks, beginning at the surface, is as 

 follows : — 



(i) Red sandstone, 20 to 40 feet thick. 



(2) Yellowish (calcareous) sandstone, 200 to 350 feet. 



(3) Whitish sandstone, probably 400 to 500 feet. 



(4) Yellow sandstone, thin layer. 



(5) Reddish-brown sandstone, more than 1000 feet. 

 The uppermost stratum has been largely eroded, and' 



remains onlv as widely separated flat-topped buttes 

 scattered about the plain. 



This upper stratum of red sandstone still existed at 

 the place at the time when the crater was formed, 

 for it is the material of the upper part of the rim. 

 It has been raised 140-180 feet above its original 

 )5osition. The upper part of the interior of the crater 

 consists of sandstone cliffs, the lower part of talus. 

 The lower portion of the latter is covered with hori- 

 zontallv stratified sediments having a total thickness 

 of 60-100 feet and a nearly level upper surface of 

 circular outline and 1800 feet in diameter. The 

 material must have settled in a shallow fresh-water 

 lake once occupying the crater. 



