Notice of Jackson on Geographical Arrangement, 6fc. 133 



a little distauce from it, but which appear to have once been its immediate 

 limit, the Bergs. Tlie terra Banks he confines to the lateral limits of the 

 stream, actually washed by its waters j the Border is the ground immedi- 

 ately above the water's edge. The Brink is the actual edge of the 

 stream, and the Margin that space, often of considerable extent, between 

 the berg and the brink. 



These terms, many of which we shall have occasion to make use of in 

 our future geological descriptions, will be best understood by a few local 

 examples. 



The Severn is a stream of at the least three orders of ramifications, that 

 is, of the third class. Its primary recipient, after a course generally south- 

 westerly, of from 250 to 300 miles, falls into the Bristol Channel. Its 

 principal ramifications of the first order are, on the north, the Neath, the 

 Taafe, the Rhymny, the Usk, and the fVye • on the south, the Parrot, the 

 Brue, the A.re, the Yea, the Avon, (Bristol,) and the Avon, (Worcester- 

 shire). Of these, many of the second order of ramifications are not named, 

 even in the best maps : the Taafe receives the Ely and>the Lesser Taafe, 

 the Avon, the Froom and the Boyd, whose subordinate ramifications are 

 not named. 



The exact embouchure of the Severn is undetermined ; its breadth at the 

 influx of the Avon is about five miles ; its main channel depth at low water, 

 about forty feet j and its length, from its origin on Plinlimmon to this point, 

 about 250 or 300 miles. Its current is rapid, and its tide-rise, flowing to 

 Upton, about seven feet. It is navigable for barges of fifty tons, and 

 drawing three foot water, as high as Welshpool. 



At Gloucester is a SrawcA-island, formed by the separation and anasto- 

 mosis of two branches of the stream ; and lower down are several channel- 

 islands, of which the Denny and the Chapel rock are ^erf-islands. The 

 mouth of the river is studded with banks. At the mouth of the Avon is 

 the Suash, a deltoid i«M/i-island. 



The bed of the Severn is chiefly rocky, though covered in many parts 

 with alluvial mud, to the depth of twenty or thirty feet. The channel is 

 very irregular, and much intersected by banks. 



The bergs of the Severn are lofty ranges of hills, occasionally at a dis- 

 tauce of eight or nine miles from the stream j near Bristol they are formed 

 by tiie ranges of 'I'horubury, Kingsweston, and Clevedon, and on the oppo- 

 site side by tiic corresponding ranges of Monmouth and Glamorgan. The 

 margins arc entirely flat and alluvial, lying about two or three feet above 

 high water. The banks are for the most part muddy, except where the 

 rock crops out, or an occasional beach of shingle is throwii up. The 

 border forms a low cliHf, about six feet in heiglit, fringed with a layer of 

 scanty reeds and grass, and alternately encroached upon by the stream, or 

 added to by tiie muddy <lc|)osits from its waters. 



Such arc some of the principal points laid down by Col. Jackson, towards 



