206 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



[vol. 50. 



It must be remembered that this fall is very old; just how old it is 

 impossible to say, but oil the now apparently plausible assumption 

 that it was contemporaneous with the formation of the crater, it 

 must antedate the latest eruption of the volcanoes north of Flagstaff, 

 since, as Mr. Tilghman informs me, the borings have shown that 

 the fine lapilli. scattered universally over the plain, occur likewise 

 over the bottom of the crater. This places it back several hundred 

 years at least. During this period the general surface of the plain 

 must have been cut down appreciably, both by wind and water 

 action, and the irons and heavier pebbles and boulders are thus left 

 exposed. 



Dr. Farrington's statement 1 that the meteoric irons "are found 

 only at the surface" is, if not founded upon a misapprehension, at 



Fig. 48 



least misleading. It is true that those thus far found lay on or near 

 the surface, but this the writer believes is due to their having been 

 uncovered by erosion. As a matter of fact, nearly all — even those 

 of but a few ounces in weight — are still covered by earth, with only 

 a mere point of iron projecting, and one not experienced in finding 

 them may pass repeatedly over a given area without success, while 

 the experienced will pick them up almost under his very eyes. 



The shale balls, in varying stages of formation and destruction, 

 are thus gradually brought to light, and, no longer confined by the 

 compact envelope of earthy matter, go quickly to pieces, and no 

 recognizable trace of the metallic portion remains. 



1 Am. Jour. Sci. (4), 17, 1907, p. 308. 



