Affinity between Bafaltes and Granite . 63 
than in our fmail experiments; we actually fee it producing 
glafs and cellular fpongy fcoria: : when the products are of a 
different character, we muft have recourfe to acceffory circum- 
fiances, and not violate the plained: rules of philofophifing by 
attributing different effeds to the fame caufe. The latent mo* 
tive for fuch an extraordinary hypothefis may eafilybe divined; 
the obferver took it for granted, that all granite is of aqueous 
formation ; hence he was obliged to reafon backwards from 
the unknown, that of the Alps for inftance, to the known* 
inflead of proceeding from the palpable effeds of fubterraneous 
fire by eafy fteps to a general theory of granite. When it Is 
taken for granted, before examination, that granite cannot be 
formed by fire, there remains no refource but to fay, that gra- 
nitic * lavas are granite rocks fufed, but not altered in the 
arrangement of their conftituent parts. 3. Though the heat 
of volcanos be fometimes and in fome places moderate ; in 
others we have good reafon to believe, that it exceeds any de- 
gree we can produce, except by means of faditious air ; we 
are certain that it forms molten currents of petrofilex and flint 
exadly the fame as our gun flints +• 
If we admit this reafoning, the appearance of granite in the 
bofom of volcanic defolation may, if duly examined in all its 
circumftances, afford ftrong evidence of its produdion by fufion ; 
and it is reafonable to conclude, that it was once covered to a 
confiderable depth by erupted matters, which the courfe of 
* “ Les laves blanches de 1 ’Ile Ponce paroiffent appartenir plus particuliere- 
ment au granit et aux roches feuilletees granitiques. On reconnoit les fubftances 
qui conftituent ordinairement ce genre de roche compofee dans prefques toutes les 
matieres blanches (volcaniques) de cette ifle ; favoir, le quartz en grain, le mica 
noir ecailleux et le feldfpath plus ou meins pur, Dolomieu, /, c, p. 8g» 
f Idem ibid, p. 107. 
time. 
