99 



On the contrary, should the effects t\rrn out to be totally 

 different, we have a conclusive argument in support of 

 the negative. 



Whether this mode, of bringing the question to issue, 

 did not occur to the gentlemen, who support the volcanic 

 origin of basalt; or whether they did not like to commit 

 a favourite theory to so rude a test, 1 will not presume 

 to conjecture. Direct evidence, with a view to the ques- 

 tion, I admit, I have none; yet, by an attentive exa- 

 mination of different writers on volcanic subjects, I find 

 pretty good light is thrown upon this topic. The evi- 

 dence I will adduce, is, I confess, indirect, and the men- 

 tion of the subject incidental: yet I do not, therefore, 

 give it less weight; for, since I engaged in polemic na- 

 tural history, I have discovered, that a reliance on posi- 

 tive assertion, is not the surest mode of obtaining truth. 



The first evidence I shall produce, to the effect of actual 

 glowing lava, upon calcareous substances, is that of Lord 

 Winchelsea: whose letter to King Charles II. (quoted by 

 Sir William Hamilton), giving an account of the great 

 eruption of ^tna in 1669, says; " Where the streams of 

 " lava meet Avith rocks and stones of the same matter, 

 " (as many are), they melt, and go away with the fire. 

 " Where they meet with other compositions" (calcareous, 

 no doubt)j " they turn them to lime or ashes." 



Mr. Ferber's testimony on the subject is decisive. He 

 gives us, in his eleventh letter, a catalogue of ejections 

 from Vesuvius; of which No. 6 is, by his account, 



" white 



