428 Proceedings of Boy al Society of Edinburgh. [sess. 
summit of a huge cone rising abruptly from the bed of the 
Atlantic, the islands being surrounded at no great distance by 
depths of over 2500 fathoms. This cone, on which the Bermudas 
are situated, was originally — there is little doubt — a volcano. No 
trace of volcanic rock has as yet, however, been dredged from its 
slopes ; it is now completely covered by a mantle of carbonate of 
lime — the broken shells and skeletons of marine organisms. It 
will he noticed that four colours surround the Bermudas. The 
inner colour (yellow) shows the coral reefs and Coral Sands and 
Muds. Outside these, the Coral Mud passes into a Pteropod 
Ooze (pale green colour) with increasing depth and distance from 
the islands. Though only shown in one small patch to the east of 
Bermuda, future investigations will probably show that Pteropod 
Ooze occurs all round the cone in depths of about 800 to 1400 
fathoms. Beyond the depth of about 1400 fathoms, the Pteropod 
Ooze passes into a Glohigerina Ooze (pink colour), and, with increase 
of depth, the quantity of carbonate of lime shells and skeletons 
becomes less and less till the Glohigerina Ooze passes, at depths 
between 2700 and 3000 fathoms, into a Bed Clay (brown colour), 
in which deposits in the greater depths there may be scarcely a 
trace of the carbonate of lime shells. 
It will be observed that the Red Clay occupies all the deeper 
parts of the bed of the ocean in this region, and covers the greater 
part of the area represented by the map. In passing towards the 
shallower depths, in the direction of the coasts of the United 
States and the West Indies, it will be noticed that a band of 
Glohigerina Ooze (pink colour) occupies the bed of the ocean from a 
depth of about 2100 fathoms up to 500 or 600 fathoms, the deposit 
varying much in composition according to depth and position. 
The deposits close to land, and generally within the 500 or 
600 fathoms-line, show great variety dependent on position 
and the nature of the adjacent land. Off the coast of Florida, 
just beyond the 100 fathoms-line, there is a deposit of glauconitic 
sand and mud (dark green colour), containing generally about 50 
per cent, of carbonate of lime. In this deposit some remarkable 
phosphatic concretions have been found,* and similar phosphatic 
* See Murray, Bull. Mus. Comp. Zool ., vol. xii. p. 42, 1885 ; also 
Agassiz, Three, Cruises of the 1 Blake? vol. i. p. 276, 1888. 
