78 



AQUEOUS AGENCIES. 



course of the streams which issue from them, are generally found ex- 

 tensive deposits of this substance. Being found mostly in volcanic 

 regions, these springs are commonly hot. 



Kinds of Materials, — The material thus deposited is usually called 

 travertine, but is very diverse in appearance. If the deposit is quiet, 

 the material is dense ; if tumultuous, the material is spongy ; if no 

 iron is present, it is white like marble ; but if iron be present, its oxida- 

 tion colors it yellow, brown, or reddish. If the amount of iron be vari- 

 able, the stone is beautifully striped. If objects of any kind, branches, 

 twigs, leaves, are immersed in such waters, they are speedily incrusted, 

 often in the most beautiful manner. 



Examples of such deposits are found in all countries. At the baths 

 of San Vignone, Italy, a carbonated spring issuing from the top of a 

 hill has covered the hill with a stratum of 

 white, compact travertine 250 feet thick. 

 In the conduit-pipe which leads the water 

 to the baths, the deposit accumulates six 

 inches thick every year. A similar deposit 

 of travertine occurs at the baths of San 

 Filippo. At this latter place, beautiful 

 facsimiles of medallions, coins, etc., are 

 formed by placing these objects of art in 

 the spray of an artificial cascade. 

 In Virginia, around the " Old 

 Sweet " and the " Red Sweet " 

 Springs, and in the course of the 

 stream which 

 flows from them 

 for several miles, 

 a brownish-yellow 

 deposit of traver- 

 tine has accumu- 

 lated to the depth 

 of at least thirty 

 feet. The spray 

 of Beaver Dam 

 Falls, about three 

 miles below the 

 springs, incrusts 

 every object in its 

 reach with this 

 deposit. 



In California, all about the shores of Lake Mono, abundance of 

 beautiful and strangely-branched coralline forms are found, which 



Fig. 73.— Deposits from Carbonated Springs. 



