4« 6 Seeond Appendix. 2d, The affinity and order that fubfifts between the different Itrata often evince a Neptunian ori gin : thus if we fee a hard ftone paffing by imper* ceptible degrees into a fofter which is not of volca- nic origin (or vice verfa), and this into clay, and the clay into quartz, we may fairly conclude that the firft in theferies is not voicanic. This mode of inquiry has been invented and fuccefsfully pur- fued by Mr. Werner. $d, As the Neptunian is by far the moft general origin of ftones, it may always be prefumed, un- til proofs of a voicanic origin be adduced. CH AP. IV. Of Stones to which a Voicanic Origin has been improperly afcribcd. Of Shorls, or Bafaltines, and White Gamets. It is now generally agreed among voicanic ob- fervers, that the fliorls found in lavas (more properly called bafaltines) pre-exifted in the'rocks which were the mother ftones or bafis of lavas before the eruption, and were not formed by fub- fequent percolation through, and cryftallization v