i88o.] 
777 
Working v. Fighting. 
Oncidium , and the author’s speculations on their origin. But 
space forbids any further remark or exposition, save of Prof. 
Semper’s hypothesis of coral formations, which cannot be 
passed over in silence. 
Few men of general reading are in these days ignorant of 
the theory now generally received on this subjedt. It was 
first propounded by Mr. Darwin in his “Naturalist’s Voyage,’* 
and explained more in detail in his subsequent treatise on 
the “Structure and Distribution of Coral Reefs,” and was 
independently discovered by Prof. Dana.* Its leading points 
may be shortly recapitulated as follows : — There are three 
great classes of coral reefs, atolls, barriers, and fringing 
reefs. The first kind are ring-like reefs enclosing a lagoon 
or tradt of water ; the second class “ either extend in straight 
lines in front of the shores of a continent or of a large island, 
or they encircle smaller islands; in both cases being sepa- 
rated irom the land by a broad and rather deep channel of 
water, like the lagoon within an atoll.” The fringing reefs 
where the land slopes abruptly under water are only a few 
yards in width, but where the slope is gentle there may be 
a channel — usually narrow and shallow — between the coral 
formation and the land.f Mr. Darwin’s theory is that the 
atolls and the barrier reefs are founded on and intimate areas 
of subsidence, the coral polypes building in shallow water and 
working upwards as the foundation subsides. Fringing reefs, 
on the contrary, show that the shore must either have re- 
mained stationary or have been elevated. 
Professor Semper, during a somewhat prolonged residence 
in the Pelew Islands, has been led to decidedly different con- 
clusions. In these islands he has found shallows without any 
reefs closely bordering on atolls. The west coast of this group 
is steep, whilst the eastern shores slope very gradually down. 
According to the Darwinian theory there should hence be a 
fringing reef on the western side and a barrier on the eastern. 
The reverse is the aftual case. On the eastern side there is 
a fringing reef, whilst on the western is found a barrier reef 
four or five miles from the land, and interrupted by three 
channels which do not lie opposite the mouths of rivers, or 
even of streamlets. He considers that the occurrence of 
large detached blocks of coral at the outer margin of all the 
reefs on the western side, the large, almost. horizontal sub- 
marine plain to the north of Peleliu, the uninterrupted con- 
* See Journal of Science, 1875, p. 534- , n f . 
+ Journal of Researches into the Natural History and Geology of the 
Countries visited during the Voyage of H.M.S. Beagle. By C. Darwin. P. 472. 
