Functions of' the Limnoria Terebrans. 329 



ment of the timbers supporting the temporary wooden beacon, 

 in which the intrepid engineer and his assistants resided dur- 

 ing a great part of the time that they were engaged in their 

 hazardous labours. I shall only state, that the temporary bea- 

 con was supported by twelve large beams of Memel-jfir, fixed 

 in batt-holes cut for them in the rock ; the sides of which beams 

 were charred and pitched ; but their soles, being closely opposed 

 to the rock, it was thought unnecessary to protect in a similar 

 manner. 



In the course of the second summer's operations, that is in 

 1808, it was found that the edges of these timbers were in a 

 state of decay, and on examining into the cause, Mr Stevenson 

 detected the limnoria in its borings. Subsequently, the logs of 

 Norwegian pine, laid down to support the temporary railways, 

 were discovered to be very much destroyed. In 1807, when 

 first placed, these timbers were ten inches square, and in 1811, 

 by the ravages of the limnoria, they had been reduced, to seven 

 inches, or at the rate of about an inch in the year. And the 

 house-timbers were so much perforated, that, in several instances, 

 they even stood clear of the rock, depending only upon the 

 stanchions and bolts for their support. * 



I have already mentioned, that it was from the Bell-Rock that 

 Mr Stevenson first sent specimens of the hmnoria to Dr Leach. 

 The same scientific engineer, not long afterwards, having had 

 occasion to examine the timber-bridge of Montrose, found the 

 piles supporting it to be very much destroyed by the borings of 

 the same animal, so that the stability of the whole structure was 

 seriously endangered. Sheathing of the new piles with sheet- 

 copper was adopted as a preservative measure, with partial 

 success. Mr Stevenson saw also the most destructive effects 

 produced by the limnoria on the gates of the sea-locks of the 

 Crinan Canal, which were thereby rendered so inefiicient for 

 their purpose, that " the locks lost seven feet of their depth of 

 water in the course of the night."" 



The next instance of the ravages of the limnoria, of which 

 I know any thing, occurred at Trinity chain-pier, in this neigh- 

 bourhood. The piles supporting thisuseful erection were, in 1825, 



• Stevenson's Account of the erection of the Bell Rock Lighthouse, p. 332 



