BOCK.3 OF THE TR A PP-FORM ATIO*. \\\ 



' VI. 



Examination of the fuppqfed igneous Origin of the Rocks of tht 

 Trupp-formation. By Mr. Robert Jameson. From tht 

 Author. 



Sheriff Brae, Leith, Sept. 8, 1S02. 



That the Bocks of the Trappformation hare been depofited from a Aqufous origin 

 State of Solution and Sufpenfwn in Water, is a Truth, which has u ao .,_f ormat j on# 

 been demonjlrated by the Wernerian Geognofie. 



IT is not at prefent my intention to ftate the proofs of this 

 opinion : the fubjed of the following obfervations is the exa- 

 mination of Mr. Playfair's account of thefe rocks. 



At fection 61- of his illuftrations of the Huttonian theory, he prof - Playfair'* 

 obferves, "The columnar ftructure fometimes found in that thVcoNminar ^ 

 fpecies of whinftone called bafaltes, is a fact which has given form of bafaltis 

 rife to much difcuffion ; and it muft be confefled, that though tcau^tt fcen 

 one of the moft finking and peculiar characters of this foffil, is in lavas, 

 not that which gives the cleared and directefl: information con- 

 cerning its origin. One circumftance, however, very much 

 in favour that bafaltic rocks owe their origin to fire, is, that the 

 columnar form is fometimes aflumed by lava actually erupted 

 from volcanos. Now, it is certainly of no fmall importance to 

 have the fynthetic argument on our fide, and to know that ba- 

 faltic columns can be produced by fire ; though no doubt, to 

 give abiblute certainty to our conclufion, it would be neceffary 

 to fliew, that there are in nature no other means but this by 

 which thefe columns can be formed. This fort of evidence 

 can hardly be looked for ; but fince the power of fufion to 

 produce the phenomena in queftion is perfectly eftablifhed, 

 and fince the production of the fame phenomena in the humid 

 way is a mere hypothefis, if there be theleaft reafon to fufpect 

 the action of fubterraneous heat* as one of the caufesof mine- 



ralization^ 



* The phenomena of volcanos and hot fprings are confidered by 

 ProfefTor Playfair as proofs of a fubterranean heat, imconnected 

 with the decompofition of any mineral fubftance. The Wernerian 

 geognofie, however, has fhewn us, that volcanos and hot fprings ori- 

 ginate in the neweft flott trapp-formation, therefore we have fuffi- 



cient 



