176 



GEOLOGY. 



[S€^t. VI. 



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and no one is so favonrably circumstanced for making 



ft 



them as a naval officer on a survcyiiig expedition. The 

 limits of depth under different latitudes at wliich the 

 variuas marine animals live or are found strewed dead, is 

 perhaps the must important point for further investigation 

 which can be suggested in the science of geology : scarcely 

 any observations with the dredge have been made witliin 

 the 



tropics. Not only the shells, corals, sea-urchins, 



crabs 



&c. 



9 



brought 



s, 



up from different stated depth 

 siiould be pi^eserved, but the proportionate numbers of 

 each kind be carefully noted, as well as the nature of 

 the sea-bottom. An observer could not labour too much 

 in this line, and especially if he would subsequently him- 

 self undertake to tabulate and work out the results,* 



There is another point of view under which the bed of 

 the sea v/ould amply repay long-continued observations. 

 t is well known that the nature of the bottom often 



changes very regularly in approaching a 



ly\> «^^ .-^V m 



th 



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pebbles, for instance, increasing in size in a surprisingly 

 steady ratio with the decreasing depth. But the means by 



which the pebbles are thus sorted is not known : is it by 

 the oscillation of the waves at ordinary periods, or only 

 during gales ; or is it by the action of currents ? A chart, 

 with the l]^'ture of the bottom carefully noted on it and 

 the currents laid down, would by itself throw some lidit on 

 tms question. The nature of the pebbles being observed, 

 perhaps a point would be found whence they radiated. 

 xccllent observations have been made by engineers on 

 the travelling of shingle beaches, but scarcely anything is 



* The best kind of dredge, and the manner of using it, are described 

 under the Zoological Section. 



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