650 



PROCIEEDINGS OF THE NATIONAL MUSEUM. 



VOL. XXXIl. 



(Ill) Puiniceous variety. 



SiO, ...: 95.22 



AlA 



FeA 



CaO 



Ign 



Loss at 100° 



0.59 

 0. 19 

 1.99 

 1.20 

 0.40 



99. 59 



A part of the linio in Analysis III was there as a mechanically 

 admixed carbonate. The high ignition (0.99) in II would suggest 

 that a part of the silica is in the condition of opal, as alread}' noted. 

 Eliminating the ignition and the free calcium carbonate in III, it is 

 evident that there is no essential chemical difl'erence in the three 

 samples. They vary as little as would probably three independent 

 ai-alyses of any one of the t3^pes from slightly different sources." 



As to the exciting cause of this metamorphism. So far as the writer 

 has information, no more satisfactory theory has been advanced than 

 that of the Messrs. Barringer and Tilgbman,^ who ascribe it to the 

 impact and incidental heat of an enormous mass of meteoric iron 

 which constituted a portion of the well-known Canyon Diablo fall. 

 Startling as it may seem, the writer, without intending to commit 

 himself in any way, has to acknowledge that it must at least receive 

 consideration, for the simple reason that nothing else seemingly worthy 

 of consideration presents itself. That there must have been intense heat, 

 and that, too, only for a brief period, is certainly manifest. The 

 force of impact of an ordinar}^ meteoric mass, as is well known, is not 

 great and the depth of penetration but slight. The majority of those 

 that come to our earth are, however, following it in its orbit about 

 the sun, and their speed on entering our atmosphere is, so far as 

 determined, only some 3 to 10 miles a second. If, however, we con- 

 ceive a mass — as from the Leonides — meeting the earth head on, as it 

 were, it would enter our atmosphere with an initial speed of 45 miles 

 a second. If such a mass were of sufficient size to escape anything 

 like complete destruction through burning, its force of impact would 

 be enormous. Whether it could or did produce the effects described 

 is, perhaps, yet an open question. 



«At the time Mr. Gilbert was making his investigations a chemical analysis was 

 made by W. H. Melville, of the vesicular variety (No. IID. This Mr. Gilbert 

 has placed in my hands. It is as follows: Si02-89.71; AI2O3-I.2O; FeO-b.34; CaO- 

 4.22; •MgO-0.22; K,O-0.15; Na2O-0.24; Co.,-3.25; Ign.-0.74; loss atl00°-0.20. Total, 

 100.27. 



'^Coon Mountain and its Crater. Proc. Acad. Nat. 8ci., Phila. 1905, p. 885. 



