50 PliOr. EDWARD HULL, LL.D., r.R.S., P.G.S., ON 



generally free from any external or artificial ingredients, 

 hence it may be regarded as the chief source of supply of 

 the carbonates and salts found in streams and rivers. If we 

 enquire what is the origin of spring water, the reply is 

 simple. It is water which originally falling on the surface as 

 rain or snow has percolated downwards into the rocky crust, 

 and taking up the soluble matters with which it comes in 

 contact, bursts forth at the surface along lines of fault, fis- 

 sure, or other natural ducts. The relative proportions of the 

 ingredients of sea water and of rivers or lakes may be 

 gathered from the following selected examples: — 



