R-QCKS OF THE TR A PP-FOR M ATION. JJ^ 



produced by the flaty clay, fandfione, or gravel. It is equally- 

 impoffible to explain vvacken veins by this hypothefis of Pro- 

 feffor Playfair. . • • 



From fection 255 to 259 is principally occupied in endea- Wedge-fhape ir- 

 vouring to (hew, that from the wedge-fhape irregularities in {2* ntlcs ° 

 thicknefs, and the frequent great inclination of beds of bafalt, 

 they would not have been depofited from a ftate of iblution 

 in water. 



To explain the appearances defcribed in thefe fections will accountcd f° r by 

 be no difficulty to the Neptunian, they are what he daily meets ^0", an un _" 

 with, and are illuftrative of the depofition of thefe itrata from equal furface $ 

 water. Let us conceive a bed of bafalt depofited upon an un- 

 equal furface, that the water breaks it (either before it has be- broken by water} 

 come folid, or afterwards) into fhapes refembling thofe de- 

 fcribed by Profeflbr Playfair, afterwards that fandfione is de- and fandftone de- 

 polited upon this broken bed ; and we have a complete pic- P ofited thereon, 

 ture and explanation of the wedge-fhape, irregularities in the 

 thicknefs, and every variety of inclination of the itrata of bafalt. 

 This is illuftrated by figure 1 and 2, Plate VIII. 



Avery flrong objection has been made to the igneous origin Objection to the 

 of bafalt and grunftone, which has always appeared to me 1^°"^°™" 

 completely unanfwerable : it is this : If thefe rocks had been that it is not 

 formerly in a ftate of complete fufion, they mould either ap- &£%J££* 

 pear as glafs, or as a fimple mafs, not containing any fubftance dies, 

 of a different nature from the mafs itfelf. 



Mr. Playfair, at the conclufion of his obfervations on the p. sir James 

 trapp-formation rocks, remarks, « Notwithflanding all this Hairs ex P eri - 



1 , , r , 1 • , • r ment * adduced 



accumulated and unaniwerable evidence for the igneous for- \ n ^ roo f t t h at the 

 mation of bafaltes, (the evidence I have examined in the preceding ft° n y character 

 pages) a great objection would ftill remain to our theory, were fu|o n , UC1 e y 

 it not for the very accurate and conclufive experiments con- 

 cerning the fufion of this foffil; made by Sir James Hall. A 

 flrong prejudice againft the production of any thing like a real 

 ftone by m eans of fufion, had arifen even among thofe mine- 

 ralogies who were every day witneffes of the ftony appear- 

 ance affumed by volcanic lava. They ftill maintained, on the 

 authority of their own imperfect experiments, that nothing but 

 glafs can ever be obtained by the melting of earths and ftones, 

 in whatever way they are combined. 



An ingenious naturalifr, after defcribing a block of bafaltes, 

 in which he difcovered fuch appearances as inclined him to 



admit 



