THE DEEP-SEA FAUNA. 161 
a former occasion. The present comparison does not extend 
so far. 
Thanks to the researches of Professor Duncan on the fossil 
corals of the West Indies, we can carry our comparison of the 
living corals into the tertiary. 
The earlier tertiary fossil corals of the West Indies have but 
little specific affinity with existing species, and there is some 
difficulty in comparing the two, owing to the varying condi- 
tions of preservation in which the fossils are found. This is 
especially the case in the raised coral beds, which follow the old 
shore lines, as indicated by the terraces seen at Barbados and 
many other islands of the Caribbean. These contain a limited 
number of species of corals generically and specifically identical 
with the present West Indian coral fauna. According to Dun- 
can the fossil West Indian corals are related on the one side to 
the coral fauna which flourished in the odlite, and on the other 
to a fauna, the first appearance of which is uncertain, but which 
attained its greatest development in the miocene, and is now 
represented in the Pacific Ocean and its associated seas. In 
deep water some of the species with Pacific affinities still live. 
From the oldest periods the faune of successive reefs had few 
species in common, but genera were most constant and persis- 
tent; and it seems clear that physical conditions which are now 
absolutely essential to the formation of coral reefs existed dur- 
ing the mesozoie and cainozoic periods. The presence of these 
conditions enables us to rebuild the geography of the past, and 
to imagine in the time of the trias a succession of larger and 
smaller islands far from continents or large rivers, but having 
deep and shallow seas, such as we now find in coral areas. The 
simplicity of the physical conditions and their continuance 
from one age to another seem a natural explanation of the uni- 
formity which has evidently prevailed in all coral regions from 
the earlrest times to the present day. 
These conditions offer a ready explanation of the more north- 
ern extension of the areas of coral reefs, of their disappearance . 
1 * Paleontological and Embryological Association for the Advancement of Sci- 
Development," Address at the Boston ence. 
Meeting (for 1880) of the American 
