120 PROCEEDINGS OF THE COTTESWOLD CLUB 



gases such as carbonic acid gas and marsh gas, the nitrogen 

 they contain passing through the form of ammonia to 

 nitric acid. They serve as food substances to hving 

 organisms, and their decomposition is dependent upon 

 the growth in the water of bacteria. These micro- 

 organisms in appropriating a portion of the organic 

 material to their own sustenance, cause a general breaking 

 up of such material, and the process commonly bears the 

 title of fermentation. Some of the substances produced 

 during the growth of bacteria are of a highly poisonous 

 nature, but in natural waters the solutions of these are 

 infinitely too dilute in a general way to produce any effect. 

 As to other hving organisms besides bacteria, water is of 

 course liable to contain all those species of animals and 

 plants that find their natural habitat in the fluid. 



Differences in Quality due to Geological 

 Origin 



All the fresh water of the earth being derived from 

 rain, has to pass over or through the various rocks upon 

 which the rain falls, and is affected in different degrees 

 according to the solubility or general nature of the 

 rocks and the soils that cover their surfaces. Thus a 

 knowledge of the geology of a district allows of a fair 

 estimate being made of the quality of the water likely to 

 be found there. We know that very little is likely to be 

 yielded to water by granitic rocks, or by the slates, shales, 

 and grits so conspicuous in the Primary Systems, but in 

 the Jurassic and Cretaceous Systems vast areas of carbonate 

 of lime are found, pervious to water, and ready to enter 

 into solution in the presence of carbonic acid gas. One 

 might expect magnesia in the water on the Permian and 

 Triassic Systems, or wherever magnesian hmestone rocks 

 are known to occur, and the possibility of strongly sahne 

 waters would be associated with the New Red rocks, the 



