904 PROCEEDINGS OF THE ACADEMY OF [DeC, 



a number of hard level strata a few inches in depth running through it, 

 as though at times the water liad disappeared and the sediments had 

 become baked and indurated by exposure to the sun. Around the 

 sides of the crater this sedimentary filling is much shallower, and its 

 bottom is marked by a bed of broken rock talus which extends out- 

 ward from the edge of the central plain, dipping towards the center at 

 about six or seven degrees. How far this talus extends is unknown, 

 but at 400 feet from the edge of the central plain it is forty-seven feet 

 beneath the surface and about twenty feet thick. In the neighbor- 

 hood of the center of the hole this sheet of broken rock does not exist 

 over an undetermined area, in which the sedimentary deposit was con- 

 siderably deeper than around the edges to the depth above noted. 

 Below the sedimentary deposits in this central area, and underneath 

 the talus elsewhere, the crater is filled with powdered rock of an almost 

 impalpable fineness. In some places this is snow-white and contains 

 over 99.5 per cent, silica. Elsewhere it is of a slightly yellowish tinge, 

 and in places is cemented together by redeposited carbonate of lime. 

 Down to 300 feet below the interior plain there is no change in this 

 material. Through it is scattered sparingly fragments, more or less 

 shattered, of the three strata penetrated by the hole, namely, red sand- 

 stone, yellow limestone and white sandstone. There is no order of their 

 deposition, but the three materials are mixed indiscriminately. In 

 shaft No. 2, however, at a depth of sixty-seven feet, there is a series of 

 boulders, scattered rather thickly through the powdered silica for about 

 twenty-five feet in depth, in which the natural order of occurrence of 

 the rocks is exactly inverted. That is, fragments of the surface red 

 sandstone are the deepest, above which come fragments of the middle 

 strata of yellow limestone and at the top are situated fragments of the 

 deepest strata of white sandstone. This formation suggests the idea 

 of the surface material, having first received the impact of the meteorite, 

 started first on its aerial flight, followed by the lower materials in turn 

 as they were reached, and retained this order when falling back into 

 the hole as it was being filled up. 



In the central portions of the hole, below 300 feet, the proportion of 

 broken and unbroken sand grains among the powdered silica begins 

 to increase perceptibly, and slightly below this point meteoric material, 

 of a character which will be described below, begins to be noticeable. 

 The filling material continues to get coarser and coarser and contains 

 more and more meteoric material with the increasing depth until the 

 500-foot level is reached. This point is 900 feet below the former level 

 of thejocky plain at this point and about 1,100 feet below the crest of 



