METEOR CRATER OF ARIZONA. 321 



simply by a steam explosion accompanied by none of the usual after 

 effects of volcanic eruption. 



A few years ago, some enterprising mining men, tempted by the 

 alluring thought of an abundant supply of nickel-iron which might 

 prove of commercial value, began a systematic series of borings from 

 the bottom of the crater, accompanied by the sinking of a few shafts 

 and the digging of numerous trenches in the material forming the 

 crater rim. These operations afforded facilities for investigation not 

 before available, and led the present wi'iter to take up the subject 

 anew. It is proposed here to give in brief, the results of these investi- 

 gations, the details of which have been largely published elsewhere. 



The prevailing formations in the region are a carboniferous 

 limestone (the Aubrey limestone of the U.S. Geological Survey), 

 somewhat arenaceous, and of a buff colour; this is some 300 ft. in 

 thickness; underlying this is a light gray, highly siliceous, saccha- 

 roidal sandstone some 500 ft. in thickness, and under this again, a 

 red-brown sandstone, the thickness of which at this immediate locality 

 has not been determined. At intervals over the surface are small 

 residual buttes of a red-brown sandstone that once covered the entire 

 region. These rocks all lie approximately conformable and horizon- 

 tally, and little changed by dynamic or metamorphic agencies. 



The crater-like depression is limited almost wholly to the Aubrey 

 limestone and sandstone, though occasionally a little of the red or 

 butte sandstone is involved. As seen from a distance, this crater 

 appears as a low, very irregular ridge of light gray colour, sufficiently 

 differentiated from the red buttes to be very conspicuous to the 

 trained eye (slide 1). Nearer approach shows it to be composed 

 mainly of fragmental material — -limestone and sandstone — in masses 

 varying from the finest dust to blocks weighing thousands of tons, all 

 in a state of greatest confusion. This rim is at its maximum some 

 160 ft. above the level of the surrounding plain. Standing upon its 

 crest one's eye is greeted by the remarkable view shown (slide No. 2) 

 - — a nearly circular crater, f.ome 500 ft. in depth and 4,000 ft. in 

 diameter, with precipitous, in places overhanging, walls, and a floor 

 of many acres covered around the margin by talus, and throughout 

 the central portions by wind-blown sands and lake bed deposits. The 

 crater walls as seen from the inside are formed of the sharply 

 upturned edges of the limestone, capped by sand and loose blocks of 

 the limestone, from the crater interior. Little of the underlying sand- 

 stone is visible in these walls, owing to the friable nature of the same 

 and to the talus fallen from above (slides Nos. 3 and i). Owing to the 

 aridity of the region, there is little vegetation, and the wild, barren 

 ruggedness of the scene is impressive in the extreme. It is, however, 

 the question of the origin of this remarkable, and apparently wholly 

 unique feature that must concern us here. 



An examination of the outer rim, as above intimated, shows the 

 same to be composed wholly of fragmental material which was plainly 

 ejected from the crater itself. Huge, rugged masses of rock, thou- 

 sands of tons in weight, down to particles of microscopic proportions, 

 are scattered in wild profusion over areas of several square miles. 

 The larger blocks are wholly of limestone, but this is due in large 

 part to the friable nature of the sandstone, which causes it to dis- 

 integrate rapidly under the trying conditions of a desert atmosphere 



V 



