l}g ROCKS OF THE TR A PP-FOR MATION. 



admit its igneous consolidation, rejects that hypothecs, merely 

 from the imaginary inability of fire to give to any fubftance a 

 ftony character : " Quelque melange," fays he, " de terres 

 que Ton fuppofe, quelque foit le terns que l'on emploie, il eft 

 tres certain que l'on n'obtiervira pas, par la feul fluide ign£, ni 

 bafalte, ni rien que lui refemble." 



Sir James Hall's experiments have completely demonftrated 

 the contrary of what is here aflerted ; they have added much to 

 the evidence of the Huttonian fyftem ; and independently o| 

 all theory, have narrowed the circle of prejudice and error." 

 It is anfwered, Sir James Hall, however, has only fliown, that when bafalt, 

 !j at Slr J a ™ es grunftone, or wacken, are completely melted and then 

 lite and the ori- flowly cooled, the glaify character difappears, and the mafs 

 ginal flone are a fTumes that of indiftinft chryftallization. This chryftallized 

 mafs he denominates chriftalite, as bearing a mofl ftrik- 

 ing refemblance to the natural ftones. To the ory&ognoft, 

 however, the glafs and the indiftinclly chryftallized mafs are 

 equally different from the original ftone, therefore the argu- 

 ments drawn from thefe experiments, in favour of the igneous 

 origin of the rocks of the trapp- formation, are unfounded, and 

 the objection which has been now fiated remains in full force. 

 Objections to Sir Sir James HalPs opinion, that lava has been in a flate of 

 iifon^that lava'" com P^ ete fufion, and by flow cooling has acquired its prefent 

 has been in a character, is probably incorrect. The well known facts, that 



frfcnf LT^^ lava has run int0 the fea ' rivers > and lakes > without aiTuming 

 the glaify character; that iflands compofed of cellular lava 

 have been formed in the fea ; and laftly, the low degree of 

 heat poiTefled by lava ft reams, (hew, that it has not been in a 

 ftate of complete fufion; on the contrary, the following facts, 

 which are to be found in the beft writers on volcanos, render 



Wernerian opi- tne Wernerian opinion, viz. that the fluidity of lava has rarely 



nion, that lava is exceec i ec i the ftate of vifcidity, extremely probable. 



than vifcid * *• Lava flows very flowly, even over confiderably inclined 



fupported by its planes. 



2. In the European volcanos glafs has hardly ever been 

 obferved. The Obfidian of Iceland, as defcribed by Bergman 

 and Olafsen ; that of Lipari ; the glafs of Vefuvius mentioned 

 by Brierlac, are moft diftinctly produces of water, as can be de- 

 monftrated by the Wernerian geognofie. 

 and the fcarcity 3. The chryftals of hornblende and felfpar, which are fofre- 

 of glafly matter, q Uen tly found in lava, being wrapped up in it (eingewickelt), 



prove, 



