Xliv IxNTRODUCTION. 



arts, 01' even as articles of food, must not be overlooked. 

 On many shores the harvest of the deep is anxiously looked 

 after, and as carefully attended to as that of the land, and 

 indeed the last is often dependant on the former for its 

 abundance. The first and most obvious use of sea-weed 

 is for manure, and to this purpose all kinds are applicable. 

 On many of our coasts, as along the west of Ireland, the 

 poorer classes are almost entirely dependant for the culti- 

 vation of their potatoes on the manure afforded by their 

 rocky shores and frequent gales of wind. After a storm 

 they may be seen congregating in numbers from the sur- 

 rounding country, with horses and cars, or with panniers ; 

 and the poorest, who cannot afford the assistance of a 

 donkey, are themselves bearers of burdens, eagerly collect- 

 ing what is thrown up and carrying it beyond the reach of 

 the tide. The kinds preferred for potatoes are the large 

 and succulent LaminariecB, which rapidly melt into the 

 ground, and when these are abundant other kinds are neg- 

 lected. These are often carried many miles into the interior, 

 and, being mixed with sea-sand, form an excellent manure, 

 which must however be used quickly, as it very soon de- 

 composes, and the gases it gives birth to are consequently 

 lost to the ground if it be suffered to lie open. 



But it is for the manufacture of kelp that marine plants 

 offer the largest revenue to man. Kelp is an impure car- 

 bonate of soda, mixed with the sulphate and muriate of 

 the same alkali, and with some combinations of iodine and 

 extraneous matter. It is prepared by merely burning the 

 weeds, previously dried, in pits dug along the shore, till 

 they are reduced to hard, dark-coloured cakes, in which 

 state it is sent to market. On our shores the species used 

 for this purpose are Fucus nodosus, vesiculosus and serratus, 

 Himanthalia lorea, Laminaria difjitata, bnlbosa and sac- 

 charina, and Chorda Jilum ; but all the large Fucacem arc 



