896 PROCEEDINGS OF THE ACADEMY OF [DeC.,, 



to an extreme state of subdivision. It seems to have been produced 

 principally from the white sandstone, for it is mostly as white as snow 

 and consists of over ninety-nine 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, although 

 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 wearing or rounding are anywhere 

 visible upon its particles. In some areas the material is composed of 

 this material exclusively and it gives no internal evidence of the man- 

 ner of its production. But in other localities it can be found contain- 

 ing a greater or less percentage of broken sand grains among it which 

 have escaped being crushed out of all recognizable shape. A continu- 

 ous series of material can be found containing more and more broken 

 sand grains and less and less silica (as we have gotten to call the impal- 

 pable powder, for want of a better short descriptive name), and then 

 more and more unbroken sand grains, and then little bunches of sand 

 grains still adhering together, and so 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 c^uite imitated 

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

 powder thus produced are more blunted and roimder 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. 



The Interior of the Hole (resumed). 



In the central area over which the talus does not extend, the line of 

 the original surface upon which the talus was deposited, and on which 

 the subsequent filling, which now covers this and also a portion of the 

 talus, was deposited, can be very readily recognized. All the material 

 lying above the talus, and above this surface, is horizontally stratified 

 and contains organic remains, such as small shells and no (or but very 

 few and small) rock fragments, while that below this line has no trace 

 of stratification nor of organic remains and contains many rock frag- 

 ments. In one shaft a beautiful series of rock fragments was observed 

 about twenty feet thick and about twenty feet below the talus, in which 

 the natural order of the rock in place was exactly reversed ; that is, the 

 red sandstone was deepest and the yellow limestone and whitish sand- 



