334 



PARK WELLS NEAR BUILTH. 



These interesting phenomena do not, however, cease with this transverse section, for 

 we can follow the same masses on their strike to the south-west, through the low hum- 

 mocks on the left bank of the Wye till they disappear at the Park Wells, where they 

 clearly explain the means by which those powerful mineral waters are formed in the 

 laboratory of nature. 



Park Wells. — The trap of this district appears for the last time on the south-west in 

 a low knoll north-west of the Pump House. It is a coarse greenstone containing many 

 crystals of iron pyrites. The Pump House stands upon this rock, but the mineral 

 water rises from the adjoining schist, which is thrown up into vertical strata striking 

 north-east and south-west, is highly charged with crystals of iron pyrites, and has in 

 parts, veins of quartz crystals and calc spar. The natural decomposition of the pyrites 

 which must be constantly going on by the percolation of water along the planes of these 

 vertical beds, sufficiently accounts for the origin of these strong sulphureous waters, a 

 natural process which has been already sufficiently explained in the account of the origin 

 of the Cheltenham waters. (See p. 34 et seq.) 



Within a very few paces of the highly sulphated spring there is another source in 

 which no sulphur exists, but in which slight chalybeate properties are alone distin- 

 guishable. 



The position of the rocks readily explains this fact. 



Builth Wells. 61. 



a. Trap. b. Altered flags. c. Unaltered flags, 



b*. Strong saline, issuing from the altered flags, 

 c*. Slightly saline water issuing from the schist. 



The sulphated spring issues from those highly pyritized and altered flagstones in 

 immediate contact with the trap, and from the vertical position of the strata and their 

 hard nature it is quite manifest that such as the spring has been from the moment at 

 which it issued to the atmosphere, so it must run on unchanged as long as pyritous 

 matter remains in sufficient abundance to impregnate it ; for the column of sulphurous 

 water rises to the surface in a natural conduit (6), which has been rendered impervious 

 upon its sides by the induration of the mineralized strata. 



At a few paces further from the trap are other strata (c) less altered, containing much 

 less pyrites, and the water rising through these is very slightly saline. In the trans- 

 verse section of these same beds in the Wye we have shown how frequently and 

 rapidly the mineral characters of the strata change in passing over their vertical edges, 

 and consequently there can be no difficulty in imagining, how very different may be the 

 contents of springs which issue within a few feet of each other. 



I use the term pyritized in reference to these altered rocks in contact with the trap 

 which contain numerous and large crystals of iron pyrites (sometimes also in flattened 

 nodules of one and one and a half inch in diameter) , because it appears to me that the 



