{ 49 ) 



they adhere to the tongue, have the confifl* 

 ence of clay, but do not emit its odour. 

 They feem to be fimple lavas, no extra- 

 neous bodies appearing in them. . It is ob- 

 fervable that every fracture is conch oidal ; 

 and that, when ftruck, they caufe a found 

 fimilar to that of fome kinds of petrofilex ; 

 which has induced me to fufpedt they belong 

 to that fpecies of ftone : a fufpicion which is 

 confirmed by examining deeper within the 

 fradtures ; fmce at the depth of two feet, or 

 thereabouts, a grey colour takes place of the 

 white, and the other external appearances 

 diminifh ; the lavas begin to aflume a fili- 

 ceous afped,and give a few i^arks withfteel. 

 Still deeper we perceive without the leaft 

 doubt that thefe lavas have a petrofiliceous 

 bafe, and contain a few {hoerls, which do not 

 appear in the decompofed parts, probably 

 becaufe they are themfelves decompofed. 



Thefe obfervations, which were made on 

 fome lavas of a black colour on the furface, 

 are likewife true of feveral others, which, 

 externally, are of a reddifh white. The ap- 



V0L» in. E pearances 



