1825.] . the Diluvium of Jamaica^ ^O }^ 57 



BeneaSii*tiii^Wuvium, but above the white hmest^neafor^aa^- 

 tion, an ambiguous conglomerate occurs, which, from the supe- 

 rior degree of its consolidation, it seems difficult to refer tO;the 

 diluvial period : the pebbles, however, very closely resemble 

 those which are certainly the products of that geological era. 

 The Vere plain, like that of St. Dorothy and Liguanea, is 

 boundedj whei'e it touches the sea, by alluvium and mangrove 

 trees. "^ '' ,,,;j '■-,'■■... :i 



There are other diluvial districts in Jamaica ; the above ar«^, 

 however, sufficient for my present purpose, which is merely to 

 show that the diiuvium of Jamaica has been produced by similar 

 causes with the diluvium of Europe, which latter I have had 

 opportunities of examining in the British Isles, France, Italy, 

 Germany, &c. I ^»ii' 



As connected with this subject, it may be as well to notiee 

 the valleys formed in the white limestone hills and mountains : 

 these present the usual varieties observed in other parts of the 

 world ; yet instances are rare in which water will be found to 

 flow through them ; the white limestone formation is in fact 

 extremely cavernous, and the rains that fall, which, it is well 

 known, are very heavy in the tropics, are received intoinnumep^^ 

 able sink holes and cavities, and disappear ; sometimes, but 

 rarely, again rising and flowing for a short distapce, again to be 

 swallowed up. The districts occupied by this cavernous lime- 

 stone are very extensive, and their places are generally shown 

 on a good map of Jamaica by a want of rivers ; whereas the 

 latter are abundant among the other rocks. Here we have 

 instances of valleys, several of which are of very considerable 

 depth, without running waters in them ; they could not, there- 

 fore, be formed by the waters which now traverse them, since 

 there are none which do so : these valleys, then, are completely 

 opposed to the theory that valleys owe their origiu to the 

 streams or rivers which now run through them. 



A valley of denudation is seen at Williamsfield (the .property 

 of Lord Harewood) in St. Thomas in the Vale. The caps of the 

 hills, or rather mountains, on either side are formed of y*^hite 

 limestone in nearly horizontal beds ; these rest on porphyritic 

 and other trap rocks forming the bottom of the valley in which 

 the Rio d'Or flows. This valley is, therefore, similar (as far as 

 respects denudation) to the valleys formed in the green sand and 

 lias near Lyme, and the green sand and new red sandstone near 

 Sidmouth ; for there would appear no more reason to doubt that 

 the white limestone near Williamsfield had once been joined by 

 strata now swept away, than that the green sand of the hills in- 

 the neighbourhood of Sidmouth and Lyme, had once >be^n CQtt- - 



tinUOUS;. ^' .i'i>\»i3' ". \' :?iO-W*'*'' .^ifiOia^TJI ar- :..;■.:■■« i ^5 



During my residence in Jamaica I visited, among other '^ 

 caverns, that most celebrated, which is named Portland Ca,ve, 



