64, DR. H. B. GUPPY: 
for my part, I never thought important at all, that is, with regard to 
the formation of submerged reefs up to the level of the sea. That 
has been so amply proved that it does not appear to me to be 
important. It has always appeared to me that there are two 
fundamental things in the growth of coral reefs which must 
take precedence of all others, first that corals grow most 
abundantly and luxuriously wherever they get most food. I think 
that might almost apply to the human populations as well as to 
coral formations. Wherever there is abundance of food and other 
favourable conditions, coral reefs will most be found. ‘Then, again, 
whenever life loses its hold of the coral structure which has been 
built up by the coral animals, whenever death ensues, inorganic 
changes commence their operations. It matters not whether this 
is assisted by creatures that bore into the solid structure, or whether 
it is due to the inorganic action of the sea. I think that by these 
general principles you can generally explain almost all the 
appearances that coral reefs present. However, there are a great 
many varieties and a great many differences due to locality. 
Temperature and the kind of food are two of the most important. 
For instance, you neyer find coral reefs except in those places where 
you have pure ocean currents. They are either found in mid-ocean, 
or off those continents or islands where the pure water is driven in 
upon the shores. The reason, of course, is the abundant supply of 
food that comes from the open ocean, driven by the trade winds. 
As to the question of barrier-reefs, when I read my original paper 
on that subject, it never occurred to me to guard what I said with 
respect to shallow and deep water. Whether itis that I had been 
accustomed to talk of deep water, Ido not know; but I always 
considered that anything under 100 fathoms was shallow water. 
My view is that banks are formed at the lower limit of breaker 
action, but that the depth varies very greatly. Take, for instance, our 
own coast. Off the north end of the Butt of Lewis, where you have 
the whole extent of the Atlantic Ocean sweeping against the north 
of the Butt, you find that the sea is in motion down to 150 fathoms. 
The great waves that come across the Atlantic wash upon the shore, 
and you have moving sand and mud; but, if you go to the north- 
east, where there is less extent of ocean and less depth, there the 
depth at which sediment commences to form gets less and less. 
I think the author is quite right about the large extension of the 
bank out towards New Caledonia. For instance, we know, as I 
have pointed out in a recent paper, that we have a very large area 
