686 T. C. CHAMBERLIN 



the core does not radically affect most geological and petrological 

 problems. 



The in/all of supposedly large planetesimals . — In the foregoing 

 tests it has been assumed that planetesimals normally grew to 

 about the same order of size as the chondrules, and that the dis- 

 ruptions and abrasions they suffered after reaching this size kept 

 them down to about the order of the little masses that form " shoot- 

 ing stars." Let us now consider the melting effects likely to follow 

 if the planetesimals had grown to very much larger sizes. To 

 keep as close to the actual as practicable, let us base our first study 

 on the phenomena of Coon Butte, or Meteor Crater, Arizona, 

 interpreted as the work of a gigantic meteorite, or cluster of mete- 

 orites or, if you please, the nucleus of a comet, accepting as con- 

 clusive, in the main, the disclosures of the drillings, shafts, and 

 trenches of Barringer and Tilghman. Then, let us base our second 

 study on the craters of the moon, on the assumption — made solely 

 for the sake of the study and without acceptance — that they were 

 formed by the impacts of still larger bodies. 



Case 1. The testimony of Coon Butte or Meteor Crater. — ^There 

 is no reason to think that the celestial mass whose plunge into 

 the earth formed Coon Butte was a planetesimal, because, among 

 other reasons, it came from the northward, an unlikely direction 

 for a planetesimal and because its indicated velocity was probably 

 too high. The work done by it, however, is very instructive 

 respecting the physical effects of such a falling mass under natural 

 conditions. 



The essential phenomena are a circular rim of upturned strata, 

 covered thickly by outthrown debris, 130 to 160 feet above the 

 surrounding plain, inclosing a crater nearly 4,000 feet in diameter 

 and 440 feet deep, measured from the original surface of the hori- 

 zontal sandstone and limestone from which the crater was formed 

 to the top of the present partial filling.' Crushed rock, mingled 



' The following are among the more important papers on the subject: A. E. Fotte, 

 Amer. Jour, of Set., Vol. XLII (1891), p. 413; also Froc. Amer. Assoc. Adv. Sci., 

 Vol. XL (1892), pp. 279-83; G. K. Gilbert, 13th Ann. Rept., U.S. Geol. Surv., Part I 

 (1892), p. 98; 14th Ann. Rept., Parti, (1893), p. 187; Geol. Soc. of Wash. (President's 

 Address), March, 1896; Science (N.S.), Vol. Ill (1896), pp. 1-13; O. A. Derby, 

 "Constituents of the Canyon Diablo Meteorite," Amer. Jour, of Sci., Vol. XLIX 



