LIME-STONE CATERS. 367 



springs, and the streams proceeding from them, and also by rain 

 floods passing over lime-stone soils, it must be inferred (according 

 to my views), that such waters must very quickly combine with 

 and precipitate all colouring matters, and, when not turbid with 

 earthy matter, be as transparent as water can possibly be. Hence, 

 the well known and remarkable transparency of such water is not 

 directly caused (as commonly understood) by lime being contained 

 in them but because of the other adulterations being totally re- 

 moved in combination with a part of that dissolved lime. Thus, 

 the water is not in the least made crystalline and transparent be- 

 cause of what it contains, but because of what it has been deprived 

 of. And, therefore, even after all the lime may have been pre- 

 cipitated, the water must retain its previous perfect transparency, 

 unless subsequently impregnated with other colouring matter. 



The additional supply of carbonic acid to water, which alone 

 gives to it the power to dissolve or to retain in solution even the 

 smallest proportion of carbonate of lime, is not strongly held. It 

 is given off by the lime-stone water in its partial evaporation, and 

 to every contact of atmospheric air ; and this operation is increased 

 by such agitation of the water as exposes a larger surface to the 

 air. Hence, at all rapids of lime-stone streams, there is a pecu- 

 liarly rapid and large deposition of carbonate of lime, let loose by 

 the water because of the loss of the proportion of carbonic acid 

 which before served to hold the lime dissolved in the water. This 

 precipitation and gradual accumulation of carbonate of lime, at the 

 rapids and cascades of streams, is the formation called calcareous 

 tufa or travertine, and vulgarly called "marl" in our mountain 

 region, and which is presented in great quantity, and sometimes in 

 enormous masses. 



As lime-stone water so easily parts with the carbonic acid which 

 enables it to hold lime in solution, it can scarcely be supposed that 

 any of the acid remains after the water collects and remains long 

 in the great reservoirs formed in lakes. But whether the water 

 remains impregnated with carbonic acid, and of couree with lime, 

 or has lost both, the effect is the same, and is exhibited most 

 strongly in the remarkable transparency of lakes so formed. Of 

 such, I have never myself witnessed any but of Lake George, in- 

 New York. And after the long lapse of time since my short visit 

 to this lake, I cannot remember to what extent the transparency 

 of its waters was asserted, or what my own personal observation 

 ascertained. I only remember certainly that the depth of water 

 through which very small objects were distinctly visible was very 

 great, and that no ground was left to doubt what is generally 

 asserted and received as true on that head. 



To return to the lands and waters of Prince George county. 

 The water left by heavy rains, standing in shallow pools on the 



