ior> 



operated, as in the Sweet spring valley, tossing away the upper and 

 more recent strata. 



Throughout all the region of which this portion of the profile may 

 be considered as giving merely a local representation, the thermal 

 waters, in virtue of the carbonic acid contained in them, hold in 

 solution large quantities of carbonate of lime. The carbonic acid in 

 quickly escaping from the water by exposure, permits the calcareous 

 matter to separate, and thus, as the stream proceeds, this ingredient 

 is precipitated at every step. Hence it is, that we find the channels 

 of the streams thus impregnated, covered with a hard incrustation, 

 accumulating in thickness every day, and even the stones and twigs 

 over which the current flows, becomes encased in a film of semi- 

 crystalline calcareous matter. Agitation of the water favouring the 

 escape of the solvent carbonic acid, will also contribute to the ra- 

 pidity of this accretion, and accordingly it is found, that where the 

 ripples are numerous, the deposite is comparatively abundant, and 

 what at first view seems most strange, even the ledges over which 

 the streams are precipitated in cascades are themselves built up by 

 additions of the calcareous deposite. The travertine formations of 

 these valleys, produced in the way we have just described, are in 

 some cases of immense thickness and extent. That in the neigh- 

 bourhood of the Sweet springs, has in all probability, a thickness in 

 some places of upwards of 100 feet, and every year adds slowly to 

 its amount. At the Falling spring, nearly on the route from Coving- 

 ton to the Hot springs, a still greater depth of this deposite has been 

 accumulated, and in various other places throughout tins region, 

 masses more or less considerable of the same curious formation, 

 may be met with in the valleys, and sometimes even at considerable 

 elevations on the sides of the hills. 



The travertine, like that already alluded to as existing in Jeffer- 

 son, Frederick and other counties in the valley, is capable of being 

 made highly useful in agriculture, and of yielding a lime of the great- 

 est purity and whiteness. 



In the mountains west of the point last referred to in the profile, 

 we discover the ternary series of sandstone, limestone and slate, as 

 before described; the limestones showing themselves altogether on 

 the flanks of mountains, and then only occasionally peeping forth. 

 As represented in the profile, repeated alternations in the dip of the 

 strata occur in this region, and the structure of the ridges is ge- 



14 



