84 Mr Mathcson on a new mode of constructing Harbours. 



waters in particular situations, to silt or sand up spaces which 

 have been enclosed, and upon which, by means of such inclosures, 

 a change has been made upon the currents. 



This tendency to sand up is peculiar to every situation, 

 where quantities of sand are under the influence of the tide or 

 the motion of the waters, and liable to be carried from place to 

 place in mechanical combination with the water, either by means 

 of the ebbing and flowing of the tide, or of the motion given to 

 it by particular currents ; or, by what is the most powerful of 

 all, the motion given to it by the violence of the winds. 



This motion of sand is generally in a direction opposite to 

 that in which the wind is blowing, as may be seen in standing 

 pools or lakes, where the sand, when the water is agitated by 

 the wind, takes shelter under the banks of the weather side ; 

 but this will be more particularly explained afterwards. 



In consequence of this tendency, the mouths of all rivers, 

 and flat shores, and all bays and estuaries into which the tide 

 rushes with violence, are more or less subject to the accumu- 

 lation and shifting of sand banks, if sand is to be found in such 

 situations. Examples of this may be seen by examining the 

 harbours of Aberdeen, Dundee, Dublin, and a variety of others ; 

 and it may be generally asserted, that no harbour was ever 

 erected upon a river that was not more or less subject to the 

 inconvenience of shifting sand banks at the mouth of the river, 

 or of being itself sanded up. 



The writer of these observations having been employed at an 

 early period of life in works connected with harbours, his at- 

 tention was particularly directed more than thirty years ago, to 

 the annoyance met with by the sanding up of harbours ; and he 

 saw the object frustrated, after the most expensive works had 

 been erected, in the hope that they would answer every purpose 

 expected from them. 



Never losing sight of the evil which he had observed, nor 

 ever ceasing to feel a desire to have it removed, he at last by 

 mere accident, discovered in the harbour of Pulteney Town, a 

 circumstance which led him to a corrective theory upon the 

 subject. 



An opening had been left in the inner pier for upwards of a 

 year, while the other operations of building were going on, and 





