ON ITS EXTERIOR. THERMAL SPRINGS. 203 



issue, strongly impregnated with carbonic acid, alike 

 from granite, gneiss, and the older and newer sedi- 

 mentary rocks. Springs containing acids become im- 

 pregnated with carbonates, particularly with carbonate 

 of soda, wherever waters having carbonic acid act on 

 rocks which contain alkaline silicates. ( 279 ) 



In the north of Germany, at many of the carbonic- 

 acid springs of water and gas, the still subsisting dislo- 

 cation of the strata and the character of the valleys in 

 which the springs break forth, for the most part " annular 

 valleys " (as at Pyrmont, Driburg, &c.), are particularly 

 striking. Friedrich Hoffmann and Buckland almost si- 

 multaneously gave to such depressions the very character- 

 istic name of "valleys of elevation " (Erhebungs-Thaler). 



In the springs termed sulphur-waters, the sulphur is 

 by no means found always in the same combinations. 

 In many which contain no carbonate of soda, sulphu- 

 retted hydrogen is probably held in solution ; in others, 

 for example in the sulphur-waters of Aix-la-Chapelle 

 (in the Kaiser, Cornelius, Rose, and Quirinus springs), 

 the gases obtained by boiling with the air excluded, do 

 not contain, according to exact experiments by Bunsen 

 and Liebig, any sulphuretted hydrogen; and even in 

 the bubbles of gas which rise spontaneously from the 

 springs themselves, it is only in the Kaiser spring that 

 0-31 per cent, of sulphuretted hydrogen is obtained.( 280 ) 



A thermal spring, giving birth to an entire river of 

 water impregnated with sulphurous acid, the Vinegar 

 Eiver (Rio Vinagre), called by the natives Pusambio, is 

 a remarkable phsenomenon, which I was the first to 

 make known. The Rio Vinagre rises, at a height of 

 about 10,600 feet, on the north-western declivity of the 



