1905.] NATURAL SCIENCES OF PHILADELPHIA. 869 



lying accumulations of soil and wind-blown material and a certain 

 amount of talus which for the greater part has been distributed by 

 torrential action, an almost level central plain in the present visible 

 bottom of the crater. Just how far these lacustrine deposits extend 

 toward the cliffs and underneath the talus, which has been brought to 

 its present position by torrential action, has not yet been determined, 

 but enough is known to state quite positively that they cover the greater 

 portion of the surface of the ancient visible bottom of the crater. 

 As above stated, underneath this sedimentary material there is to be 

 found an incredibly large amount of what has been locally termed 

 silica, and which certainly is due to the pulverization of the sandstone 

 strata and the sand grains composing them. This so-called silica (this 

 name will hereafter be used in referring to this material) is almost free 

 from impurities ; several analyses having shown it to contain upwards 

 of 98 and even 99 per cent. SiOj. To be properly understood this silica 

 should be examined under a microscope. When so examined it is 

 found to be composed of broken sand grains ; some of the minute frag- 

 ments being as large as the half of a sand grain, but the vast majority 

 are very much smaller, and many of the fragments are so small as to be 

 invisible under an ordinary lens. Under a strong glass or microscope 

 they have the general appearance of broken pieces of ice, being of every 

 conceivable shape and almost invariably having very sharp edges, and 

 of course being translucent. Much of this so-called silica is so finely 

 pulverized that no grit can be noticed when it is placed between the 

 teeth, and in fact can be truthfully described as being an impalpable 

 powder. At many places this silica is less finely subdivided than has 

 been described above and is distinctly gritty when placed between the 

 teeth ; but at no place has there been found any particle of it which is 

 larger than one of the small sand grains which go to make up the strata 

 in which the crater is found. Without further explanation it can be 

 stated definitely that this silica is nothing more or less than pulverized 

 sandstone. How many million tons of this material there are it would 

 be impossible to estimate. It composes a great part of the enormous 

 rim, over three miles in length measured around the base of the moun- 

 tain, in which the crater is situated. The amount of it within the 

 crater is absolutely unknown; for it has been found by means of drill 

 holes to a depth of more than 850 feet. At places both on the ex- 

 terior of the rim and in the interior of the crater, underneath the sedi- 

 mentary deposits, it is found admixed with a small percentage of lime 

 carbonate, which admixture can of course be readily understood when 

 it is remembered that there is shown in the walls of the crater a calcare- 



