836 ABOUT COMMON WATER. 



it appears turbid ; sent through the South Downs well- 

 water, it appears muddy, so great is the quantity of 

 chalk precipitated by the boiling. The mere exposure 

 of hard water to the open air, where it can evaporate, 

 softens it considerably, by the partial precipitation of 

 the mineral matter which it held in solution. 



This last observation is important, because it en- 

 ables us to explain many interesting and beautiful 

 effects. In chalybeate springs, iron is dissolved in the 

 water. Round about such springs, and along the rivu- 

 lets which flow from them, red oxide of iron iron rust 

 is precipitated by the partial evaporation of the 

 water. In Iceland, the water of the Great Geyser holds 

 a considerable quantity of flint or silica in solution. 

 By a most curious process of evaporation this silica, as 

 shown by Bunsen, has been so deposited as to enable 

 what was at first a simple spring to build up, gradually, 

 the wonderful tube of the Geyser, which is seventy- 

 four feet deep and ten feet across, with a smooth basin, 

 sixty feet wide, at the top. 



Again, the great majority of our grottos and caves 

 are in limestone rock, which, in the course of ages, has 

 been dissolved away by a stream. To the present hour 

 are to be found, in most of these caves, the streams 

 which made them. I have been through many of them, 

 but tlirough none which can compare in beauty with 

 St. Michael's Cave in the Rock of Gibraltar. From 

 the roof hang tapering stalactites, like pointed spears. 

 From the floor rise columnar stalagmites. The stalac- 

 tites gradually lengthen, while the stalagmites gradu- 

 ally rise. In numerous cases stalactite and stalagmite 

 meet, the sharp point of the former resting upon the 

 broad top of the latter. Columns of singular beauty, 

 reaching from floor to roof, are thus formed. Stalac- 

 tites and stalagmites are to be seen in all phases of their 



