VOL. XXVI.] PHILOSOPHICAL TRANSACTIONS. 405 



they may go the farther, and then dig trenches about 6 or 7 feet distance, and 

 throw the soil they take out of them on the potatoes, so as to cover them ; then 

 fencing the plot of ground, they leave them to grow. Planted in April or 

 May they are ripe in August ; they dig them as they have occasion, and let them 

 lie till next year, then dig them again, and so the third year ; every year they 

 by this means go deeper in the earth, and the last they dig them, they pick 

 them out as carefully as they can, that little seed may remain; and the fourth 

 year they plough the ground and sovi' barley, and the produce is very good for 

 some years. Some potatoes will remain and grow up, without any hurt to the 

 barley or oats ; those they dig and pick out, and the ground remains good and 

 arable ever after. 



It is observable, that shells answer best in boggy grounds, where the surface 

 is turf; for turf is generally nothing else but the product of vegetables, such as 

 grass, heath, &c. which rotting, the salt is washed away by the water, and 

 there only remains the earthy, and especially the sulphureous parts, as appears 

 from the inflammability of turf; now shells being chiefly a salt, it incorporates 

 with the sulphur of the plants, and renders them fit for the vegetation of new 

 plants. Which further appears from this, that shells that have been under the 

 salt water are much better than such as have been in the earth, or dry on the 

 strands : on digging a foot or two deep about the bay of Londonderry, it yields 

 shells, and whole banks are made up of them ; but these, though more entire 

 than such as are brought out of the shell island, are not so good for manure, I 

 observed in a place near Newtown Lamavady, about 2, miles from the sea, a 

 bed of shells, such as lie on the strand; the place was covered with a scurf of 

 wet spouty earth, about a foot thick ; the country people used the shells, but 

 they were not reckoned so good as those that are found in the sea, or near it. 



The land about the sea-side bears very indifferent wheat : nor will the shells, 

 in that respect, do without some dung; yet this may be owing to the ignorance 

 of the farmers, who generally understand nothing of wheat. Some thousands 

 of acres have been improved by the shells, ^nd that which formerly was not 

 worth a groat per acre is now worth 4 shilling^; they have in many places thus 

 improved the very mountains, that before were mere turf bogs. In these they 

 meet with this inconveniency, that if the season for ploughing proves wet, their 

 horses sink so deep in the soil that they cannot plough it, especially after two or 

 three years. 



They commonly made lime of the shells formerly, and some do so still ; it 

 binds very well, and I believe it is not so corrosive as lime made of stone ; fori 

 find that in the history of Ceylon, that they make up their land with lime of 

 oyster-shells, which I believe would be impracticable with common lime. About 



