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SUPERPOSITION. The order in which 

 bodies are placed upon or above 

 other bodies, as more recent strata 

 upon those that are older ; second- 

 ary rocks upon primary; tertiary 

 upon secondary, &c., &c. The 

 order of superposition of rocks is 

 never reversed, unless it be by 

 volcanic agency, when rocks may 

 be forced from below and thrown, 

 as it were, upon those which, in 

 the usual order of superposition, 

 would be above them. Beds, or 

 strata, may be altogether wanting, 

 but whereever similar beds occur 

 together, the order of superposition 

 is never inverted. Thus the Wealden 

 deposites are never found above the 

 chalk ; the chalk is never found above 

 the London clay; the London clay 

 is never found above the crag: nor 

 do we meet with the chalk under 

 oolite, the lias under the red sand- 

 stone, or the coal under the grey- 

 wacke. The order of superposition 

 alone does not form a certain cri- 

 terion of the ages of rocks, but 

 when coupled with their zoological 

 contents, the two connected may be 

 considered the only safe criterion. 



SUPRA-CRETA'CEOUS. (from supra, above, 

 and cretaceus, chalky, Lat.) Above 

 the chalk ; formations more recent 

 than those of the chalk. The 

 supra-cretaceous deposites are very 

 commonly termed tertiary. This 

 is, however, a name exceedingly 

 objectionable, as it would imply 

 that there were three great classes 

 of rocks possessing marked charac- 

 teristic distinctions, and that the 

 deposites above the chalk consti- 

 tuted the third of such classes. 

 The supra- cretaceous rocks consti- 

 tute a large portion of the dry land 

 of Europe, among the lowest of 

 which, in Western Europe, are those 

 of the London and Paris basins. 

 Bakewell considers the term supra- 

 cretaceous, or, as he writes it, 

 super- cretaceous, to be peculiarly 

 inappropriate, and adds, " if a new 



name were necessary, post-creiace- 

 ous should have been chosen." 

 The supra-cretaceous rocks are ex- 

 ceedingly various, and contain an 

 immense accumulation of organic 

 remains, terrestrial, freshwater, and 

 marine. This group has lately 

 been shown to approach, more 

 closely than was supposed, to the 

 existing order of things on the one 

 side, and to the cretaceous group 

 on the other. 



SU'RTURBRAND. A name given to 

 Bovey coal, or brown coal. 



SU'SSEX MA'RBLE. A member of the 

 Wealden group; occurring in 

 layers varying from a few inches 

 to upwards of a foot in thickness, 

 the layers being separated by seams 

 of clay, or loose friable limestone. 

 It is a fresh-water deposit, and 

 contains in great abundance shells 

 of paludinse, a genus of fresh-water 

 univalves. It is of various shades 

 of grey and bluish-grey, mottled 

 with green and yellow ; it bears a 

 high polish, and is used extensively 

 for architectural and ornamental 

 purposes. There is historical proof, 

 says Dr. Mantell, of its having been 

 known to the Romans, and in the 

 early Norman centuries it was 

 much sought after, and applied, 

 when cut into small shafts of pillars, 

 which were placed in the triform, 

 or upper arcades, of cathedral 

 churches, as at Canterbury, Chi- 

 chester, &c. The archiepiscopal 

 chair of Canterbury cathedral is 

 formed of Sussex marble. 



SU'TURE. (sutura, a seam, Lat.) A 

 seam ; the junction of the bones of 

 the head by an irregularly jagged 

 zig-zag line. 



SWAL'LOW. The name given to a 

 chasm or hollow, commonly occur- 

 ring in the mountain or carbonifer- 

 ous limestone, in which a stream of 

 water is engulphed. The stream 

 or river reappears after a certain 

 subterranean course. 



SWI'LLEY. A provincial term for a 



