OF THE VAlilOUS LEAD-SPAllS. 
513 
and other favourable circumstances, an opportunity is of- 
fered for the formation of crystals ; or it may be deposited 
in a massive form. I may observe farther, that galena, 
abounding with such patches of the other lead-spars, is, 
in general, what is brought from a considerable depth, 
thus affording full opportunity for the operations I have 
pointed out going forward. 
I am aware of the objections which may be brought 
against my hypothesis, in consequence of the insolubility 
of the lead -spars, in the menstruum stated to be the 
principal agent in these operations ; but when it is recol- 
lected that silica (a substance of equal insolubility) fre- 
quently occurs in many natural craters, the objection, I 
apprehend, will not be considered a very valid one. 
I have stated my ideas to most of those engaged in the 
works here, and I now feel myself warranted in saying, 
that their opinions (and these I consider valuable) coincide 
generally with that I have myself formed, and which I 
have now communicated to you. 
I have frequently conversed on the subject with Profes- 
sor Irving, whose acquirements in science, and residence 
here for twenty years as agent for one of the companies, 
have afforded him ample opportunity of forming correct 
ideas ; and these, I am happy to say, agree with my own. 
I hope the few observations I thus offer, may induce 
others, more fitted for the task, to direct their attention 
more particularly to this subject than has hitherto been 
done ; and any further observations I may have an oppor- 
tunity of making shall be most readily communicated to you, 
I remain, &c. 
James Braid, 
Leadhills, ) 
March 4. 1823. J 
