18G0.] WALL VF.NKZI r.r.v AND TRTXIDAD. 469 



resembling sinter, often agatifbrm or chalcedonic. Probably a 

 solution is occasionally discharged in which the hydrate of silica is 

 dissolved by carbonic acid and sulphuretted hydrogen : <>n arriving 

 at the surface the excess of these gases would be volatilized, and 

 the siliceous matter precipitated in more or less hydrated forms. 

 There was no evidence of the silica having been combined with an 

 alkaline base, a condition under which it has often been supposed that 

 that substance passed into solution. The surface, quite devoid of 

 vegetation, is occupied by a sandstone, also of the "Older Parian" 

 series; instead of the usual reddish shade, however, it is of the purest 

 White, evidently from the bleaching action of the acid waters. The 

 mode in which the various tints are communicated to the siliceous 

 substances can be very distinctly traced, since the only sources of 

 colouring matter proceed from the sulphur deposited from the water, 

 and the carbon and mineral principles of the decaying Leaves which 

 are blown from the adjacent woods. The yellow colours are due to 

 the sulphur, and the brown and other shades to the vegetable matter. 



Additional manifestations of the same nature are stated to exist in 

 the vicinity ; but the opportunity for their inspection was not afforded. 

 These phenomena, including the thermal waters, may be due to the 



same chemical activity, producing different results according to the 

 nature of the strata traversed by the vapours and fluids. The 

 derivation of the dissolved silica may perhaps be attributed to the 

 cementing substance of the sandstone, the more or less hydrated 

 condition of this cement rendering it susceptible of solution in heated 

 acidulated waters. 



These suppositions also readily explain how, in two adjacent 08868, 

 the deposits should be exclusively calcareous in olle, and equally 

 siliceous in the other, thus corresponding with the mineral oharacti r 

 of the rock in which the agencies occur. 



Tin' respective areas occupied by the three groups constituting 

 the territory embraced within the 8th and loth parallels, and the 



(list to 69th meridians, may be approximately estimated as — 



tqoare noHea 



Caribbean 



< Oder Parian ( Lower Cretaceous ) . 



Rewer Parian (Miocene ?) 36,500 Llanos. 





1 tal. . 54,000 



- .. ral memorable earthquakes have agitati d the northern littoral 

 of Venezuela, de s tr oyi ng Cumani in IT'.'" and Caracas in 1812. 

 A severe convulsion affected the former town and a Large extent of 

 the adjacent surface on the L6th August, L868. The shock, which 

 occurred at 2 p.m., with a duration of more than 50 seconds, is de- 

 scribed as proceeding from uorth-easl to south-west with a horizon- 

 tal progression, and terminating by vertii al oscillations. In ( 'nm ami 



■ !y a house remained uninjured, and the Larger build 

 as the foxtj bridge, college, and ohurcfa i utirely demolished. 



