VOLCANIC THEORY UNTENABLE 497 



fumarolic or solfataric phenomena. With all the careful study, there has 

 not been found the least evidence of any volcanic or igneous activity of 

 any kind. The nearest volcanic phenomena are at the San Francisco 

 mountains, about 15 miles distant. Further, the pulverized character of 

 the rock debris, described below, is not consistent with the idea of an 

 explosion nor with the digestive action of heated waters. The explosive 

 or volcanic theory has not a single fact to stand on. On the other hand, 

 the investigation has developed several remarkable facts which are well 

 explained by the impact theory of the crater genesis. 



The powdered Sandstone, "Silica" 



It has been found that the greater part of the enormous mass of rock 

 debris or ejectamenta on the outer slopes of the crater rim is a very fine, 

 white, quartz powder ; and the same material occupies the pit, beneath the 

 inwashed beds, to the depth of several hundred feet. This "silica" 

 (using the term common on the ground) is certainly only the crushed 

 white sandstone. Much of it is as fine as flour, 50 per cent of it passing 

 through a number 100 sieve, but under the microscope it shows its char- 

 acter as crushed crystalline quartz. Quoting from Mr Tilghman (page 

 896) : 



. . . "it is mostly as white as snow and consists of over 99 per cent 

 silica, although here and there small areas or deposits will be of a slightly 

 yellowish color from the yellow limestone and contain a little carbonate of 

 lime (althoiigh this has to a great extent been leached out of it), and much 

 more rarely of a reddish color, either stained by or produced from the top 

 stratum of red sandstone. Under the microscope it is seen to consist of 

 minute fragments of clear transparent quartz with edges and points of 

 extreme sharpness, and no signs of any rounding are anywhere visible upon its 

 particles. In some areas the material is composed of this material exclu- 

 sively. . . . But in other localities it can be found containing a greater or 

 less percentage of broken sand grains among it which have escaped being 

 crushed out of all recognizable shape. A continuous series of material can be 

 found containing more and more broken sand grains ... on up to the 

 solid sandstone rock. Its general microscopic appearance is identical with 

 that of a handful of glass fragments produced by a blow. It cannot be quite 

 imitated by grinding the sand grains in a mortar, as the edges and points of 

 the powder thus produced are more blunted and rounder and broken than those 

 of the silica. But it is very closely duplicated by the finest powder produced 

 by firing a high-power rifle bullet against a block of the sandstone." 



On the surface of the wreckage slopes the silica has been so removed 

 by stormwash and winds that large fragments of the several rocks occupy 

 most of the present surfaces, in size up to thousands of tons (see plate 



