322 PROCEEDINGS OF SECTION C. 



and upwards of 5,000 ft. above sea-level. An important feature is the- 

 presence in this rim of enormous quantities of crushed and bleached 

 si>.ndstone, which will be referred to later under the name of "rock 

 flour" and "ghost sandstone." Trenches and shafts which have been 

 sunk into the rim at various points bring to light only fragments of 

 the lime and sandstone, all tumbled together in the wildest confusion, 

 and Avholly without order. On the north sids of the crater there were 

 uiicovered in the trenches numerous masses of partially oxidised 

 meteoric iron, of a nature so susceptible that their preservation in a 

 moist climate has proved a matter of the greatest difficulty. These 

 occur in such association with the rock detritus as to leave no doubt 

 but that they were thrown out of the crater together and at the same 

 time as the materials in which they occur. 



In the early stages of the exploring operations, two shafts were- 

 sunk in the bottom of the crater. These, after penetrating something 

 like 100 ft. of wind-blown material and lake bed deposits, passed 

 into a mass of rock flour formed from the smashing of the sandstone, 

 which presented such mechanical difficulties to the work that the 

 shafts Avere abandoned and recourse had to borings. From these 

 shafts there were, however, brought up occasional peculiar, white 

 and platy or spongy masses of rock, Avhich microscopic and chemical 

 examination showed to consist of true quartz glass, resulting from the 

 fusion of the crushed quartz, and of a completely recrystallised rock, 

 consisting wholly of quartzes Avith a Avell-developed rhombohedral 

 cleaA^age, and showing, optically, a condition of molecular strain. 

 This crystalline A^ariety shoAved also a secondary platy structure, such 

 as could be produced only by dynamic agencies. An intermediate 

 stage of metamorphism was shown in the so-called ghost sandstone. 



The drilling was carried on by means of iron pipes some 3 in. in 

 diameter, the cutting tool being a hardened steel bit. A series of 

 twenty-eight holes was driA^en at various points in the crater bottom, 

 the deepest extending to a depth of upwards of 1,100 ft. The 

 character of the material passed through was made evident by means 

 of a stream of water forced downward through the pipe, and ffiiding 

 its way to the surface again through the space immediately around 

 the outside of the revolving drill. The implement was not such as to 

 make the securing of a core_ in all cases possible, since not merely 

 was the boring, as a rule, discontinued, when what was bej'-ond doubt 

 solid rock, was struck, but the weight of the column of water in the 

 pipe was sufficient, on AvithdraAving the drill, to force out anything 

 that might have been otherwise obtained. In seven cases out of the 

 twenty-eight, howeA^er, small sections of cores were obtained, and 

 such were submitted to microscopic examination with the results 

 noted later. 



The general I'esult of these borings ma}"" be shown by the follow- 

 ing record from Hole No. 17 : — Feet. 



(1) Surface material, soil, sand, and wash from cliffs 0- 2T 



(2) Lake-bed formations, lying horizontally, and con- 



taining diatoms, shells of moHusks, and abun- 

 dant gy]3sum crystals ... ... ... ... 27- 88 



(3) A sand which gives reaction for nickel and iron 



and contains fragments of metamorphosed sand- 

 stone, sandstone pumice, kc. ... ... ... 85-220 



