FOR GREA T BRITAIN AND IRELAND. 65 



from any personal knowledge, but as regards the Race of Port- 

 land it exists in the smoothest weather, during the strength 

 of the current, and when there is an entire absence of wind. 

 That the collision of water with the bottom will cause 

 these great disturbances may be seen in a large fresh- 

 water river, far above the level of the tide, and where 

 no undulation exists, as, for instance, at a weir on a river 

 down the incline of which the water glides with accelerated 

 speed, after passing the ridge or upper edge. At the foot 

 of such a weir the writer has seen a wave of fresh water 

 rise as much as 5 feet, and for a hundred yards beyond the 

 water is greatly disturbed, causing quite a miniature race. 

 This raging of the water is clearly caused by its overfalling 

 in the case of the river, without any swell, all disturbance 

 being primarily caused by the weir, answering to the ledge 

 off Portland Bill, and the other uneven ground in the 

 vicinity. When this disturbance occurs on a shoal off the land 

 some distance, it is known as an " overfall " instead of a 

 race, the overfalling of the water and recoil of the force 

 from the bottom resulting also in a tumultuous sea. Until 

 the water is carried by the current over the edge of these 

 banks, it is often in fine weather-almost as smooth as a river, 

 and the tumult rises up immediately the edge is past. 

 This action of the water can be daily observed at the mouth 

 of tide rivers on the ebb, and particularly on the flood tide 

 inside the bars, some distance above which the current, in 

 falling into the channel over the steep sides of the banks, 

 causes a similar disturbance on a reduced scale, and may be 

 seen higher up the estuary, also at the steep edges of other 

 banks. Although the swell of the ocean encountering and 

 opposing a tidal current, is a most severe aggravation of the 

 raging of the sea whenever it occurs, it is not the universal 

 cause of such races, because they exist constantly without it. 

 VOL. IX, E. 4. F 



