25 1 Olservations regarding Dykes and Veins. 



the Earth's crust into very numerous piles of strata, almost or* 

 entirely separated from each other, by these original fissures: the 

 greater part of which, originally open fissures, have, since, been 

 (symnietricaHy filled up, by layers or ribs of mineral matters (of 

 very numerous kinds in diirercnt cases) applied successively 

 against the skirts, until the fissure was filled ; producing thus, 

 almost universally, the appearances of nearly vertical newer strata 

 or ribs*, intersecting and dividing the original strata, almost per- 

 pendicular to their planes ; some of which ribs, are nearly pa- 

 rallel to each other, and others curved, and forming often, very 

 suddenly, lenticular masses, in the fissures which had previously 

 been open. I have in no instance been able to discover clear 

 marks, of mechanical violence having dislocated the piles of 

 strata, prtidius to the filling up of the Dykes and veins : but since 

 that well marked period in the history of ourStrata, a tremendous 

 external force seems to have operated, to fracture the Earth 

 anew, and dislocate its fragments; such new and dislocating 

 fractures (usually now termed faults) having passed along the 

 former fissures, in most, but not everv instance, the solid dyke- 

 stuff or vein-stuif, usually forming now one side of these second 

 or fault fissures ; and such dyke-stuff exhibiting the same marks of 

 violent grinding, as the ac^jacent edges of the fractured strata do. 

 Into these second and dislocating Jiss ares it is, that all the ex- 

 traneous matters, like real rolled pe'jbles (not nodules formed 

 in the veins), organic remains, &;c., have found their w^y from 

 the surface, both into Mineral Veins, and into Faults. The al- 

 most general fact, of the faults proving water-tiglit, and sepa- 

 rating the strata, into distinct plots or drainages, arises mostly, 

 I think, from the perfect continuity of the previous vein or Dyke- 

 stuff and its remaining entire on one side (and in some rare in- 

 stances en both sides) of the Fault, and not from the violent 

 jamming in of soft clayey matters, into the fault : yet in many 

 instances, where a mere crack or very thin fault-stuff is visible, 

 and yet proves water-tight, it would seem, that some such ope- 

 ration has taken place, as with the Sinker, who has occasion to 

 blast in a porous rock, full of water, and has recourse to the ex- 

 pedient, of cramming his hole quite full of very stiifly-tempered 

 clay, and then very forcibly hanmiering the same in, by means 



* I dn not mean by this to be iiiulerstoutl to assf it, that any consiilcra- 

 ble portion of all the vertical strata, or tho^c veiy hii;lily inclined, which 

 aie met with, occujiy Dvkts: because in i^cntjiiil, such are occasioned hy 

 the strata having been a[jphf;d on the inchiiint; cir almost vfiiieal slope of 

 a blimp or ridge in a previously deposited stratum For it is by no means 

 necessary or true, that all strata, even the most shelly or contjli.merate, 

 must have been deposited in an /loiizuntal position: as short-sighted theory 

 has asserted. 



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