438 _ LHE POPULAR SCIENCE MONTHLY 
This study of the reefs of Cuba and the Bahamas naturally led him 
to renew his observations in Florida and to visit the Bermudas. He 
saw the Bermuda Islands in March, 1894, and in December of the same 
year he chartered a tug and steamed along the Barrier Reef of Florida. 
He found that in common with the Bahamas the Bermudas consist 
of wolian limestone. In places the interior of these islands were dis- 
solved away by the action of rain-water rendered acid by decomposing 
vegetable matter, and thus depressions were formed in the central parts 
of the islands. Then when the islands sank the sea broke through the 
rims and filled the lagoons, afterwards deepening them by its scour- 
ing action. 
Thus the Bermudas have assumed an atoll-like shape, but their con- 
tour is not due to corals. Indeed, there are but few corals at Bermuda, 
and these form a mere veneer over the sunken wolian ledges. The so- 
called miniature atolls are mere pot-hole basins which have been scooped 
out by wave action in the ewolian rock, and their rims are never more 
than eighteen inches high, and consist of a wall of eolian rock covered 
by a coating of serpule, alge and corallines which enable them to with- 
stand the wearing action of the sea. Thus Darwin’s theory of coral 
reefs can not explain the conditions seen in the Bahamas and Bermudas. 
The results of his study of the Florida Reef were finally published 
in 1896 in cooperation with Dr. Leon 8. Griswold. Agassiz concludes 
that the Marquesas, of Florida, are not an atoll, but enclose a sound 
that has not been formed by subsidence, but by the solvent and mechan- 
ical action of the sea. Thus the Marquesas are similar in their geo- 
logical history to other sounds back of the line of the Florida Keys. 
He found an elevated reef extending along the seaward face of the 
Florida Keys from Lower Matacumbe to Soldier’s Key. We now know, 
however, that the elevated reef actually extends from the southern end 
of Big Pine Key to Soldier’s Key. Agassiz believed that the oolite 
limestone back of the elevated reef and along the mainland shore of 
Key Biscayne Bay was xolian rock; but Griswold decided that it was 
only a mud-flat which had been formed beneath the water, and after- 
wards elevated. Later studies have shown that Griswold was right. 
In 1895 he instituted a study of the underground temperature of 
the rock walls of the Calumet and Hecla mine, and found that the 
increase is only 1° F. for every 223.7 feet as we descend. His deepest 
temperature observation was 4,580 feet beneath the surface of the 
ground. 
Ie had now seen all of the coral reefs of the Atlantic and turned 
his attention to the exploration of the Pacific. In April and May, 
1896, he cruised along the Great Barrier Reef of Australia in the little 
steamer Croydon, which he chartered from the Australian United Steam 
Navigation Company, Captain W. ©. Thomson being in command. 
