1 1 4 Editorial Covnr/ient. 
pletely encircling small islands, — represents so much land that 
has been carried by subsidence beneath the level of the sea. 
Out in mid Pacific again are smaller reefs similar in all respects 
to reefs that encircle the smaller islands, but in ^Dlace of an 
island each reef surrounds a lagoon or basin of clear, quiet sea- 
water. These are the atolls or coral islands proper. Darwin's 
explanation is familiar to all. The corals laid the foundations 
of the reef around the skirts of an island, but the island has 
disappeared as a result of subsidence, and its place is now occu- 
pied by the enclosed lagoon. Moreover, the lagoon would 
represent approximately the area of the lost island. Such, in 
brief, are the explanations proposed by Darwin, and such have 
been the teachings of geology for nearly fifty years. 
The theory of Murra}^ that, according to Argyll, must now 
supplant the teachings of Darwin, is based on observations 
made during the voyage of the Challenger. It requires no 
subsidence. The phenomena, according to Murray, would be 
the same whether the area were stationary or even slowly ris- 
ing. Without going into every detail, the explanation would 
be something like this: Other conditions being favorable, 
corals will establish themselves over the sea bottom, along 
shores, out to the twenty or thirty fathom limit. The outer- 
most colonies, however, have an advantage in respect to the 
food and oxygen brought by the waves. Along the outer limit 
colonies are therefore more numerous, and at the same time 
more vigorous, and the reef rises more rapidly than elsewhere. 
The animals on the outer zone exhaust the sea water of its sup- 
plies and the colonies on the inside of the upvvai'd growing rim 
necessarily perish. During the upward growth of the reef 
fragments, through the action of waves, driftwood and other 
agencies are continually breaking off from the fragile, branch- 
ing colonies, and falling down on the seaward side. A talus is 
thus formed, which, as soon as it reaches the proper bight, 
is seized as a foundation on which new colonies establish them- 
selves. The new foundation affords special advantages in the 
matter of nourishment; the seaward colonies thrive while 
those situated on the inner margin being placed at increasing 
disadvantage, languish and finally perish. In this way, accord- 
ing to Murray, coral reefs are continually advancing seaward. 
