WRECKS AND DRIFTWOOD. 201 



it is constantly receiving. By far the larger part of this 

 wood floats until it becomes waterlogged \ and this being 

 the case, when it does at last sink, it must do so too far 

 from shore to have much chance of being covered with 

 mud or sand and converted into coal. 



Seventy miles from the mouth of the Ambernoh River of 

 New Guinea, the Challenger found the sea so blocked with 

 drift-wood that her screw had to be constantly stopped. 

 Long lines of it were passed, consisting partly of whole trees, 

 but chiefly of broken pieces of wood with the stems of a 

 large kind of cane-grass, various fruits and other fragments, 

 and the seeds of inland plants, but no leaves, for these drop 

 first near the shore. A wide area of the sea in this region is 

 constantly covered with drift-wood, which seems to have a 

 special population of its own. Much of the softer vegetable 

 matter decays and dissolves and so helps to feed the whole 

 kingdom of Protozoa as well as more highly organised forms 

 of animal life. But the wood might last for ages under water, 

 if there were no means of getting rid of it except by the 

 slow process of decay ; for one of the old wooden ships of 

 the Northmen has been lately dug up from the place where 

 it sank and was buried some thousand or more years since, 

 and oak is still in existence which is known to have been 

 driven into the bed of the Thames in the time of Julius 

 Caesar, nearly two thousand years ago. 



But neither wrecks nor drift-wood are left to accumulate, 

 thanks mainly to the curious teredo or " ship-worm," which 

 is really a bivalve having a very small shell, only a few lines 

 broad in fact, while its greyish-white worm-like body is a foot 

 long and half an inch thick. This creature bores deep 



