CH. n ON BOASD H.M.S. 'FLYING FISH' 27 



the inaccuracy of our charts and the want of knowledge 

 about the tides which sweep the reefs. 



We have abundant evidence to show that charts of coral 

 reefs made one year are almost valueless twenty years 

 afterwards ; and nevertheless we have at present absolutely 

 no experimental results to indicate to the navigator or the 

 naturahst in what places the reefs are growing seaward, and 

 where they are gradually breaking down. 



In such a passage as Banka Strait, the force of the tide 

 is strongest near the middle of the channel, and feebler 

 towards the shores. Let us now suppose that at some 

 point upon the coast the average tidal rate was the most 

 favourable one for coral growth. This particular point 

 would have a tendency, I beheve, to grow out slowly into 

 the strait. The rate of growth would be more rapid in 

 shallow water than in deep water, but under all conditions 

 it would grow until it reached that part of the current 

 which was too strong to be favourable to coral growth, and 

 there it would stop ; while the sides of the projecting reef 

 thus formed would grow until they reached the same strong 

 currents. A change in the force or direction of the tides 

 of the strait due to the change of reef in other places, or 

 volcanic disturbances, might cause this reef to progress 

 stni further into the strait, or, on the other hand, to com- 

 pletely die and become diminished by solution and erosion. 



My object in referring at such length to the subject of 

 the supposed growth of coral reefs has been to endeavour 

 to show that, apart from any movements of elevation and 

 subsidence of the earth's crust, the coral reefs should be 

 looked upon not as simple stationary structures, but as 

 living moving things, ever changing their form and aspect. 

 Sometimes they obtain a mastery over the waves and en- 

 croach upon the domains of the sea ; sometimes they are 

 beaten back by the tides, eroded and dissolved ; whilst at 



