GEOLOGY AND MINEEALOGY. 301 



2. Water of the Ottawa River (10,000 parts.) 

 A. Obtained. B. Calculated. 



Carbonate of Lime . 2480 



Carbonate of Magnesia 0.0696 



Chlorine . 0076 



Sulphuric Acid 0.0161 



Silica 0.2060 



Chloride of Sodium . 0607 



Chloride of Potassium 0.0293 



Residue, dried at 306^f 0.6975 



Residue, ignited 0.5340 



Carbonate of Lime . 2480 



Carbonate of Magnesia 0.0696 



Silica 0.2060 



Chloride of Potassium 0.0160 



Sulphate of Potassium 0.0122 



Sulphate of Soda „ 0.0188 



Carbonate of Soda 0.0410 



A1203, P05 

 Fe O, Mn O 



V traces. 



"The comparison of the two river-waters whose analysis we have just given, 

 shews the following differences: — The water of the Ottawa, containing little more 

 than one-third as much solid matter as the St. Lawrence, is impregnated with a 

 much larger proportion of organic matter derived from vegetable decomposition, 

 and a larger amount of alkalies uncombined with chlorine or sulphuric acid. Of 

 the alkalies in the state of chlorides, the potassium salt in the Ottawa constitutes 

 32 per .cent, and in the St. Lawrence only 15 per cent. ; while in the former the 

 silica equals 34, and in the latter 23 per cent, of the ignited residue. The 

 Ottawa drains a region of crystaline rocks, and the alkalies liberated by the de- 

 composition of the feldspar of these rocks give their character to its waters ; the 

 extensive vegetable decomposition evidenced by the organic matters in solution, 

 must alsp contribute a portion of potash ; while the basins of the great lakes 

 through which the St. Lawrence flows are excavated in palseozoic strata which 

 abound iu limestone, rich in salt and gypsum, and have given to the water of this 

 river that predominance of soda, sulphuric acid and chlorine, which distinguishes 

 it from the Ottawa. The presence of large amounts of silica in river-waters is a 

 fact but recently established. Until the analysis by Deville of the rivers of France 

 (1848), the silica in water had generally been wholly or in great part overlooked ; 

 and, as he suggests, had, from the mode of analysis been confounded with gypsum. 

 The importance in an agricultural point of view of this large amount of dissolved 

 silica, where river-waters are employed for the irrigation of land, is very great ; 

 and geologically, the fact is not less significant, as it marks a decomposition of the 

 siliceous rocks by the action of waters holding in solution carbonic acid, and the 

 organic acids arising from the decay of vegetable matter, which, dissolving the 

 lime, alkalies, and magnesia, from the native silicates, liberate the silicic acid in a 

 soluble form.* Silica is never wanting in natural waters, whether neutral or alka- 

 line, altnough proportionably less abundant in neutral waters which contain large 

 amounts of earthy ingredients. The alumina, whose presence is not less constant, 

 although in much smaller quantity, appears equally to belong to the soluble consti- 

 tuents of the waters. The amount of dissolved silica anuually carried to the sea 

 by the rivers must be very great ; yet sea-water, according to Forchhammer, does 

 not contain any considerable quantity in solution; it doubtless goes to form the 



* Although this may be true enough to a certain extent, yet, undoubtedly, a large portion 

 of the silica present in the waters of rivers, more especially of such as flow through uncleared 

 districts, is derived from the constant decomposition of the wood of fallen trees, of ferns 

 and other vegetable matters. In the ashes of most ferns, the silica is over 70 per cent., and 

 in those of equiseti, over 50 ; whilst it averages about 10 or 12 per cent, in the ashes of the 

 bark, wood, and leaves (taken together) of our common pines. E. J. C. 



