C 3 
ceedmg eTght or ten inches in breadth, on unequal 
lengths from five to thirty feet, 
, The colour, hardnefs, weight, and fnbfiance of 
thefe ftones fufiiciently fhew them not to belong to 
the genus of the marbles, amongft which Mr. Da- 
cofta ranked them in imitation of the ancients. 
Their fubfiance is vitreous, analogous to that of the 
horny ftones ; they refift aqua fortis, and the chizzel: 
and only yield to a violent fire and the engravers wheel. 
Being worked in this manner they acquire the polilh 
of the ancient bafaltes, named by the Italians Marmo 
paragone, I have not yet completed a chemical 
analyfis of thefe ftones, which they richly deferve, 
chiefly as they contain fmall nefts of cryftals of 
tin ore, yellow, green, and black. Thefe probably 
greatly contribute towards giving to our ftones their 
fingular and conftant form. They feem to have ac- 
quired that form, in a different manner from that 
which influenced the ftrata and veins of other 
mountains. Laftly, no marks or impreflions of any 
organical bodies are found either in the out or inlide- 
of thefe ftones. 
From all thefe confideratlons I was induced fo^ 
attribute their origin, to a watery cryftallifation,. 
which might have taken place, either at the firft 
fettling of the chaos, or at the time of a diflblution; 
of a great part of our globe. I had faid the fame 
thing in regard to the Giant’s Caufeway,.in my ac-- 
count of the formation of new iflands. But 1 now 
begin to entertain fome doubts about that opinion,, for.' 
thefe two reafons. 
r. In the explanation of the plates of the French! 
Encyciopedie,. 1 find that an. obfervation made by- 
