THE FISHERIES. 



caused a manifest obstruction to navigation ; but the 

 patent or charter weirs in Ireland, are soHd struc- 

 tures, and are, for the most part, situate at the very 

 top of the tideway. Great jealousy was always en- 

 tertained with respect to obstructions in the tidal 

 parts of rivers, where the sea ebbs and flows, but 

 the position of those ancient weirs was very carefully 

 chosen : since we find, in almost every case, they are 

 constructed in situations, where obstruction to the 

 navigation of the sea or tideway could not by possi- 

 bility occur; we might instance the Lismore Salmon- 

 weir, now the property of the Duke of Devonshire, 

 which is situated at least two miles above the tide- 

 way ; or, the great Salmon-fishery at Ballyshannon, 

 which is formed by a ledge of rocks at the upper 

 extremity of the tideway, where nature herself pro- 

 hibited navigation ; and we beheve all the Salmon- 

 weirs, extending across rivers, were constructed 

 above, or near the extremity of, the tideway, and 

 were founded on fords, or ledges of rocks, which were 

 themselves barriers to navigation. We have, indeed, 

 casually observed, that so nicely was this question, as 

 regards the tideway adjusted, at the original for- 

 mation of many of these weirs, that their foundations 

 appear to have been laid exactly at the point to 

 which the spring-tide reaches, and it would appear 

 that this critical selection of the site above the tide- 

 way for these permament and soHd obstructions, was 

 adopted, at a remote period, to accommodate the ori- 

 ginal structure to the requirements of the common 



