462 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vol. 50 



Proceedings of the Philadelphia Academy of Sciences. 1 Such an 

 origin was considered by Mr. G. K. Gilbert in his paper on the "Ori- 

 gin of Hypotheses," published in 1896, but the facts then available 

 failed, in his opinion, to substantiate so startling a conclusion. The 

 later developments and the interpretations put upon them have 

 reopened the question and in the minds of many proven the cor- 

 rectness of the meteoric hypothesis. 2 



The mere existence of a crater some three-fourths of a mile in 

 diameter and 500 feet in depth in a region of undisturbed sedimentary 

 rocks and remote from volcanoes is in itself enough to invite scien- 

 tific inquiry, while even the plausible suggestion that such might be 

 due to the impact of a stellar body is of so unusual a nature as to 

 warrant the fullest investigation. Consultation with the authors of 

 the paper above noted impressed the writer with the desirabiliy of 

 a re-study of the problem in the light of the new evidence. The 

 matter was therefore laid before Secretary Walcott, of the Smith- 

 sonian Institution. He promptly approved of the general plan of the 

 work, and in May of the present year the writer spent several days 

 on the ground, and has since been in frequent consultation and cor- 

 respondence with Messrs. D. M. Barringer and B. C. Tilghman, the 

 prime movers in the development work. The results are given in 

 the following pages. The closing down of the works at this time, 

 owing to the approach of winter, furnishes a convenient halting place 

 in the investigation. 



II. Geology and Physiography of Region 



The region about Canyon Diablo is an elevated and nearly level 

 sandy plain, the floor of which is composed in the main of a buff-col- 

 ored arenaceous limestone known as the Aubrey (Carboniferous) lime- 

 stone. This is capped here and there by low, elongated flat-topped 

 mesas of red sandstone, which are but residuals from a one-time 

 continuous stratum that covered the entire area. The limestone is 

 underlaid by a highly siliceous sandstone of a gray or faintly buff 

 tinge (also Carboniferous), and this in turn by a yellow, merging 

 into red, sandstone. The exact thickness at this point of any of these 

 beds can not be given. The U. S. Geological Survey, basing their 

 estimates on results of well borings at Winona, some 30 miles distant, 



1 Coon Mountain 'and Its Crater, by D. M. Barringer, and Coon Butte, by 

 B. C. Tilghman, Proc. Acad, of Sciences of Philadelphia, 1906, pp. 861-914. 



2 At the December, 1906, meeting of the Geological Society of America, in 

 New York, Prof. H. L. Fairchild, of Rochester, submitted some lantern slides 

 of the crater and announced his acceptance of this hypothesis. 



