XVI. 



AT certain parts of the Scottish coast, the ' dykes/ 

 or walls built near the road-side, are constructed 

 entirely of rough-hewn pieces of hard sandstone rock, 

 brought from the neighbouring shore. Sometimes a 

 dyke will extend for two or three miles, without 

 presenting an isolated fragment, in which the honey- 

 comb-like perforations of certain species of the boring 

 Mollusca are not more or less apparent. 



A fragment of soft sandstone lies before me, measur- 

 ing three and a half inches in length, and two inches in 

 breadth, which, small though it be, contains no fewer 

 than seventeen cylindrical tunnels. Each of these 

 exhibits so wonderful a skill in construction, that 

 human hands could not surpass it, though aided by 

 ' all the means and appliances to boot/ of mechanical 

 agency. 



It is generally stated that the Pholas never in- 

 trudes itself into the apartment occupied by a neigh- 

 bouring ' worker/ The Pholas, however, often in- 

 trudes on its neighbour ; and such intrusion is 



