AMERICAN AND WEST INDIAN FAUNA AND FLORA. 123 
know to be even now growing and increasing in thickness. Yet 
they have been mentioned by some writers as examples of a 
former continental extension ; and archeologists have attempted 
to find, on the Dolphin and Challenger ridges, the bridges, at 
depths of nearly two thousand fathoms, of the former land con- 
nections of Africa and Western Europe with Central and South 
America. There seems to be no necessity for these supposed 
Pacific and Atlantic continents, so long as we can explain by 
more simple causes the distribution of the present fauna and 
flora. 
The marked difference between the fauna of the Red Sea and 
of the Mediterranean * clearly points to a distinct separation 
between these seas — greater perhaps than that once existing 
between the Bay of Panama and the Caribbean — previous to 
the time when land masses united Malta and Sicily with Africa ; 
when Crete and Rhodes were united with Asia Minor, and there 
was no Eastern Mediterranean to reach the shores of Egypt and 
Palestine. All this shows a comparatively recent connection 
of Mediterranean with Atlantic waters, fully supported by the 
similarity, if not identity, of their marine fauna. We certainly 
find in the Eastern Mediterranean proof of the great changes 
which have taken place in the distribution of land and water 
during the tertiary and diluvial period. These changes, while 
they may in part be traced to such agencies as denudation both 
aerial and chemical, must also be referred to terrestrial changes, 
— to such volcanic or tellurie agencies as slowly raise or lower 
definite traets of country, when aeting undisturbed through 
long periods of time. We have in the Eastern Mediterranean 
a district subject to volcanic action, the force of which is 
marked by the number of active and extinct volcanoes which 
have produced in the past and are still producing very marked 
changes. The zodgeographical conditions existing between the 
northern and southern shores of the Mediterranean do not of 
1 The rapidity with which even slight way to the Mediterranean, much to the 
water communications affeet the distribu- detriment of the fisheries ; and a species 
tion of species is admirably shown in the of sea-urchin, quite common in the Red 
case of the Suez Canal. Since its com- Sea, has lately been found in the Medi- 
pletion, several species of sharks charac- terranean, near Port Said. 
teristic of the Red^ Sea have found their 
