Related Geological Condition^ 39 



The close agreement of Table i with that given for 

 granite is suggestive. The high percentage of organic 

 matter (8.75) and of sulphuric acid (8.88) in Table 2 

 over granite is readily explained when one considers that 

 the volcanic dust was ejected during Eocene times, and 

 might readily have been mixed with organic remains of 

 that period. Proof of this is given below. Again the 

 amount of lime or of iron may vary, and either may give 

 a distinct character or color to the rock formed, or cause it 

 the more readily to recombine with other rocks. Russell 

 says (p. 286) that in Nebraska volcanic dust covers twenty 

 counties, sometimes to 50 feet in depth in the southwestern 

 part of the state, but becomes gradually thinner and finer 

 when traced eastward. So the volcano must have been to 

 the south-west. 



Geikie again in quoting an earlier and graphic writer 

 says: — "A vast colunin of exceedingly fine dust rises out of 

 the crater, sometimes to a height of several miles, and then 

 spreads outwards like a sheet of cloud. The remarkable 

 fineness of the dust may be understood from the fact that 

 during great volcanic explosions no boxes, watches, or close- 

 fitting joints have been found to be able to exclude it." 



As regards the distance to which the dust may be 

 carried Bonney (/^: 189) in describing an eruption at Mt. 

 Hecla says: "one, which began in September 1845 lasted for 

 more than a year, and the ejected dust fell abundantly in 

 the Orkneys, quite 500 miles away. Copious discharges 

 of this material seem indeed to be rather characteristic of 

 Icelandic eruptions." Writing again of the volcanic peaks 

 of South America he says (p. 241) : "But the most noted 

 of all is Consequina, for it was the scene of a frightful 

 eruption in 1835 ... It began on the morning of 

 January 20th, when several loud detonations were heard, 

 followed by the ejection of a cloud of inky smoke 

 The cloud spread gradually outwards, obscuring the sun, 

 while fine dust fell from it like rain. This went on for two 

 days, the sand falling more and more thickly, and the ex- 

 plosions becoming louder and louder. On the third day 

 they reached a maximum, and the darkness became intense. 

 The quantity of material that fell was so great that for 



