874 PROCEEDINGS OF THE ACADEMY OF [DeC, 



much erosion, such as must have taken place in order to account for 

 the great amount of tahis which is to l^e olDserved on the inside of the 

 crater, supposing it to have accumulated in the usual way, the crater 



Sixth : If a steam explosion had formed this crater, it is inconceiv- 

 able to me that it would not have thrown up rocks from a greater depth 

 than that represented by the three uppermost strata, together with a 

 very small portion of the upper part of the Red Beds which underlie 

 them. Nothing would seem to be more certain than that the greater 

 portion of these Red Beds and the great Carboniferous series of strata 

 extending thousands of feet under them, as exposed by the Grand 

 Canon of the Colorado, only seventy miles distant, are undisturbed 

 In other words, the series of strata at Coon Mountain have not been 

 disturbed, at least to the extent of being thrown out, for a greater 

 depth than the upper portion of the Red Beds, geologically speaking, 

 or about 1,200 feet more or less — perhaps as much as 1,300 feet — below 

 the present surface of the plain. 



Seventh : A steam explosion I assume could not have pulverized the 

 individual sand grains, as they have been pulverized here, and produced 

 as a result the millions of tons of "silica" which exists on the inside of 

 the crater and on the outside of the rim as alreadv described. It is not 



