SIR JAMES HALL 167 



problems presented by the rocks of Scotland, Hall was 

 familiar with the views of his master, and was able 

 to supply him with fresh illustrations of them from 

 different parts of the country. Gifted with remarkable 

 originality and ingenuity, he soon perceived that some 

 of the questions involved in the theory of the earth 

 could probably be solved by direct physical experiment. 

 Hutton, however, mistrusted any attempt 'to judge 

 of the great operations of Nature by merely kindling a 

 fire and looking into the bottom of a little crucible.' 

 Out of deference to this prejudice, Hall delayed to carry 

 out his intention during Hutton's lifetime. But after- 

 wards he instituted a remarkable series of researches 

 which are memorable in the history of science as the 

 first methodical endeavour to test the value of geo- 

 logical speculation by an appeal to actual experiment. 

 The Neptunists, in ridiculing the Huttonian doctrine 

 that basalt and similar rocks had once been molten, 

 asserted that, had such been their origin, these masses 

 would now be found in the condition of glass or slag. 

 Hall, however, triumphantly vindicated his friend's 

 view by proving that basalt could be fused and there- 

 after by slow cooling could be made to resume a stony 

 texture. Again, Hutton had asserted that under the 

 vast pressures which must be effective deep within 

 the earth's crust, chemical reactions must be powerfully 

 influenced, and that under such conditions even lime- 

 stone may conceivably be melted without losing its 

 carbonic acid. Various specious arguments had been 

 adduced against this proposition, but by an ingeniously 

 devised series of experiments Hall succeeded in con- 

 verting limestone under great pressure into a kind of 



