72 DYNAMICAL GEOLOGY. 



much larger streams than now ; in nearly all cases, 

 instead of being hollowed out by solution, they are now 

 being filled again by chemical deposit. When the waters 

 were in abundance they dissolved ; but, now that they are 

 reduced to drippings, they deposit. The drippings from 

 the roof form icicle-like stalactites (a) ; the drippings on 

 the floor, the stalagmites (b) ; the runnings down the 

 walls form pilasters. The stalactites, constantly growing 

 in size and length, finally meet the stalagmites and form 

 pillars (c), (Fig. 39). 



FIG. 39. Section of limestone cave. 



The variety and beauty of the forms produced by 

 deposit in these caves are often marvelous. One of the 

 latest discovered and most wonderful in this respect is the 

 Luray Cave, Virginia, described in the " Smithsonian 

 Keport" for 1880. Fig. 40 is copied from this report. 



The caves and galleries of lava are formed in an entirely 

 different way, as will be explained hereafter under the 

 head of Igneous Agencies (page 137). 



Lime-Sinks. In cases of soft, impure limestone, the 

 undermining of the rock causes the surface to sink. 

 Thus are formed the lime-sinks so common in Florid*! 

 and some portions of Georgia. 



Chemical Deposits in Springs. Wo have seen that 

 all springs contain mineral matters in solution. Sonic of 

 these are deposited at the surface, and some not. The 

 most important deposits are lime carbonate from carbon- 



