Volltext Seite (XML)
^6o Huttonian Theory 8. Maffes .of fandftone, and flate-clay, included in veins, are ufually harder than thefe rocks aye in general*. ;; , 0 ; v 9. The fliifts.in venigenous diftri$s are of ho rn enfe extent f. , • ■ : v -t • , 10. All veins appear to ftioot from below into the fuperior ftrata. , , t,- We * “ Another mark of fufion, more diftin&ive of w.hin, is, that both in veins and in maffes, it fometimes includes 7 | pieces of fandftone, or of the other contiguous ftrata, com pletely infulated, and having the appearance of fragments of rock floating in a* fluid fufficiently denfe and poride* rous to fuftain their weight. Though thefe fragments havp been tdo refractory to be reduced into fufion themfclves, they have not remained entirely unchanged, but are, in general, extremely indurated, in compatifon of the rock from which they appear to have bee'n detached.”—Play fair'. 1 : lllujlrations, p. 7a. ■f- “ Mineral Veins, particularly at their Interfe&ions with one another, contain abundant marks: of the moft violent and repeated difturbance *. Not to mention, that they owe their fir ft formation to the fra&ure and difplacing of rocks already confolidated ; it appears, that they have originated at very different periods, and that thp birth of each has been accompanied with convulfions, which Ihook the foundations of the earth., In Cornwall* for inftance, the principal veins, and thofe which they diftinguilh particularly by the name oi\ Lodes, have near ly the fame direction with the ftrata* or vertical fchiftus, extending from about E. N. E. to W. S. W. Thefe* however, are often interfe&ed nearly at right angles* by other * Thefe marks of difturbance are flips and Ihifts in the ftrata.