THE BOCK STRATA 



495 



3. White sandstone with some j'ellow 

 and pink, about 1,000 feet. 



4. Dark red sandstone, thickness un- 

 known. 



The uncertainty as to the precise 

 thickness of the limestone is due to the 

 broken and disturbed structure of the 

 uptilted beds in the crater walls. Mr 

 Barringer gives the thiclcaess as 200 to 

 350 feet. No drilling has been done 

 on the plain outside the crater, where 

 the rocks are undisturljed. 



The Crater 



tails relating to the crater and the § 

 debris will be found in the papers by 

 Messrs Barringer and Tilghman and in 

 the earlier writings by Doctor Gilbert, 

 but only the more important facts will 

 be given here. 



The pit or "crater" is circular and 

 bowl-shaped, 4,000 feet in diameter at 

 the top, and toward 600 feet deep, 

 measuring from the rim. The upper 

 part of the walls are steep cliffs (see 

 plate 55) of limestone and sandstone, 

 uptilted so as to have a quaquaversal 

 dip of 30 to 40 degrees, and in places is 

 greatly shattered and crushed. The 

 lower part of the walls is a talus slope 

 produced by many centuries of storm- 

 wash on the broken cliffs. Just pre- 

 vious to the writer's visit to the crater 

 (September, 1906) a heavy storm or 

 "cloudburst," characteristic of the arid 

 region, burst exactly over the crater 

 and illustrated the talus-making pro- 

 cess. The northern trail leading down 

 the crater wall was obliterated and 



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