75 
of Shropshire and parts adjacent. 
port to Gloucester where it meets the tide is 89 feet, according to a 
series of levels taken by direction of the late Mr. W. Reynolds of 
Ketley. Hence it appears that the bottom of the tide at Gloucester 
stands on a higher level by about 16 feet than the tide at Chester, 
which from the form of the Bristol channel and the well known 
extraordinary height of its tides, added to the greater distance of 
Gloucester from the sea, is all very consistent with what might have 
been a priori expected. 
From the high level of the Ellesmere canal, already mentioned, a 
branch proceeds to the limeworks of Llanymynech, and is thence 
continued up the vale of the Severn as far as Newtown in Mont- 
gomeryshire. By combining the measurements thus obtained with 
the preceding ones, a number of interesting particulars concerning 
the descent of the Severn during the greater part of its course may 
be obtained, which I shall proceed to mention in some detail, as the 
rate of descent of navigable and other streams, although a most im- 
portant branch of natural geography, has hitherto been almost 
entirely overlooked. 
A number of mountain torrents, rising chiefly on the eastern 
skirt of Plinlimmon, unite at the town of Llanidloes into one main 
stream called the Severn, which from that place to its entrance into 
the plain of Shrewsbury flows north-north-east, winding through a 
a valley a mile or more across. It receives on each hand the con- 
tributions of numerous brooks and small rivers, and thus serves as 
the common drainage into which the superfluous waters of a moun- 
tainous tract of considerable extent discharge themselves. 
From Llanidloes to Newtown, a distance of at least fifteen miles 
measured along the bank of the river, are several rapids but no per- 
pendicular fall : the rate of its descent through this space I am un- 
acquainted with. During the remainder however of its course, 
k 2 
