250 Mr. A. B. Northcote on the Water of 



examined, notably before and after the accession of important 

 tributaries, and before and after changes of stratum in the river's 

 bed. From this point of view the series of analyses which I 

 proceed to give is but a contribution to a knowledge of the con- 

 stituents of the river Severn, for the specimens examined were 

 taken almost exclusively at about a mile above the city of Wor- 

 cester. I have, however, been enabled to make one analysis 

 which bears upon the question of the influence of tributaries ; 

 and among the rest will be found one made in time of extreme 

 drought and another immediately after a time of flood, which, from 

 their thus presenting nearly the limits of the river's variation, 

 have a certain value. 



The channel of the Severn, in its course of 210 miles from the 

 side of Plynlimmon to the sea, experiences many changes. Start- 

 ing from the Silurian rocks of Montgomeryshire and cutting a 

 patch of trap rock near the border, it enters the New Red Sand- 

 stone in Shropshire; at Shrewsbury it passes for a few miles 

 through the Lower Red Sandstone of the Permian group and 

 the neighbouring coal-field; it then passes again consecutively 

 through the New Red Sandstone and Silurian rocks, and tra- 

 verses in turn the great Shropshire coal-field and the overlying 

 Permian Sandstone, until at about Stourport it passes from the 

 coal-measures to the New Red Sandstone, through which and 

 the Red Marl of the same system it flows to Worcester. At 

 some distance below Worcester it cuts alternately the Lias and 

 the Red Marl before reaching the Bristol Channel. 



But although it thus passes through a considerable variety of 

 rocks, yet I believe at no part of its course does it receive afflu- 

 ents which are likely to bring to it any constituent which it 

 would not already have acquired as the Severn proper, for its 

 principal tributaries drain the same formations as those through 

 which the main stream runs. The original Hafren or Severn 

 receives at Llanidloes the Clywedog, and before it leaves Mont- 

 gomeryshire the Vyrnwy, both of which run exclusively through 

 Silurian rocks; while its other principal tributaries, the Tern 

 which falls into it below Shrewsbury, the Stour which joins it 

 at Stourport, and the Sal warp which, under the name of Hawford 

 Brook, flows into it about three miles above Worcester, begin and 

 end their course in the New Red Sandstone. The composition 

 of the river is probably more affected below Worcester by the 

 junction of the Teme, which flows for many miles of its course 

 through Devonian strata, and doubtless even more by the influx 

 below Tewkesbury of the Avon, which passes chiefly through 

 Lias ; but these may be passed over as being without influence on 

 the present inquiry. 

 The chief features, therefore, of the river's bed above Worcester 



