the River Severn at Worcester. 269 



had washed down all the looser materials of the river's banks ; 

 and the same circumstance may perhaps explain why the more 

 soluble salts, the chloride and nitrate, existed in less amount 

 than in the water of April collected after more sudden rain, 

 whilst the salts which would require a longer- continued action 

 of meteoric water for their solution or formation, the calcic sul- 

 phate, the calcic, magnesic, and alkaline carbonates, and the sili- 

 cates, were found in greater proportion. The conditions under 

 which the water of February was collected have been sufficiently 

 described. Rainfall could have had but little influence upon it, 

 for the origin of the flood was the thawing of the snow ; it is, 

 however, interesting to observe that the suspended matter then 

 brought down was little more than half that produced by the 

 sudden rain of April, and to see that the long-continued action 

 of water acted upon the strata of the district in a more marked 

 degree, but in the same direction, as was observed in October. 

 For a comparison of these actions I would refer to the Table in 

 which the percentage composition of the mineral residues of the 

 waters is given, as that exhibits the mutual relations of the dis- 

 solved constituents more distinctly. 



The few facts thus given show how greatly the character of a 

 river-water depends on the amount, and even more on the locality 

 of the rainfall. In the eight examinations of this water which I 

 have made, the most unexpected variation which I have been 

 able to trace is that of June 1858; but it is probable that 

 such changes are of very frequent occurrence. This must be 

 especially the case with such a river as the Severn, the tribu- 

 taries of which, from the varying nature of their watershed and 

 channels, necessarily come to it charged with very different kinds 

 and quantities of dissolved matter. More might therefore be 

 done in this instance to provide a town with a purer water than 

 could be effected where the supply is drawn from a river which 

 has its sources and its course in rocks of more equal solubility, 

 and which is liable to no sudden accession of rainfall from a 

 mountainous region. It would be necessary to ascertain the in- 

 fluence of all the principal tributaries on the constituents of the 

 river ; and then, with a knowledge of the rainfall at the various 

 points up the river by which these tributaries are supplied, the 

 reservoirs might be filled at such times as would ensure the col- 

 lection of a purer water. The requisite knowledge of rainfall 

 might perhaps be in time obtained by an extended telegraphic 

 system supplying a daily record which might be thus acted upon. 



The Severn differs from most rivers in the larger quantity of 

 chloride of sodium which it contains. Rivers in general are poor 

 in this constituent, as the continued percolation of meteoric water 

 has long since dissolved it from the majority of rocks and carried 



