37 



my country, (to which I confine myfelf ) are utterly irrecondleable to 

 any theory I have met with. 



Two fefts of naturalifts, diftinguifhed by the names of Vokanijls and 

 Phttoni/is, have of late taken poffeffion of all the bafalt in the world, 

 and have divided it between themfelves, under the defcriptions of erupted 

 and unerupted lava; and they have fo convinced Dr. Beddoes of the vaU- 

 dity of their claim, that he fays, " I fliall affume the origin of bafaltes. 

 " from fubterranean fufion to be thoroughly eflabliflied." 



After fuch a round affumption it may be deemed uncivil to quettion 

 the igneous origin of our bafalt Dykes; but natural hiftory is not to be 

 facrificed out of refpeft to confident affertion ; I will therefore try by the 

 tefl of fads whether that defeription of bafaltes (which your Lordfhip 

 wiflies for information upon) ever was in fufion. 



Foreigners feem to know little of Whynn Dykes except in mines. Mr. 

 S-. Fond found at Chamarelle in Vivarois, what is obvioufly a Whynn 

 Dyke, and it embarraffed him more than any fa£t he ever met with ; it 

 will be found entertaining to look into his Vol. ex. de Vivarois, and into 

 his Min. des Vol. to fee the difficulties into which this courant de lave 

 compaae this ruifeau de bafalte en fufion has thrown him, and the fwing- 

 ing poftulates he is obliged to make, in order to get over them. 



Dr. Hamilton on behalf of the Volcant/ls, and Dr. Hutton, the great 

 advocate for the Plutonic fyftem, are more ready at their expedients; 

 the firfl: of thefe forms our Whynn Dykes by pouring in erupted lava 

 at the upper aperture of mighty chafms; while Dr. Hutton conceives 

 thefe chafms were filled up by his own unerupted lava, forced up at the 



lower. 



In difcuffing the opinions of thefe gentlemen I will make them the 

 moft liberal conceffions ; for inftance, I will concede to both, that they 

 have difcovered the procefs by which nature has formed chafms of im- 

 meafurable length, immeafurable depth, and of inconfiderabk, though 

 uniform, breadth. 



I will concede to Dr. Hamilton that he has brought to the edge of the 

 chafms his lava, " this foreign fubftance, which iifuing from the vaft 



" mafs 



