REPORT Ois" THE DEEP-SEA DEPOSITS. 
379 
siderable role both in space and in time, concerning whose mode of formation there has 
been much controversy, without any very definite solution being arrived at. We propose, 
in the first instance, to point out its mode of occurrence in modern seas, its essential 
characters, its geographical and bathymetrical distribution, its organic and mineral 
associations, and thereafter to discuss the various hypotheses that have been advanced 
concerning its origin in modern seas and in geological formations. 
Mode of Occurrence and Macroscopic Characters . — Among the collections made by 
the U.S.S. “Tuscarora” along the coast of California are several specimens of dark green 
or black sands composed almost entirely of grains of glauconite, a little less than a mil- 
limetre in diameter. There were a few Foraminifera and mineral particles other than 
glauconite, of about the same dimensions, mixed with these dark green grains. If the 
samples which we have examined were in the same condition as when procured from the 
bottom of the sea, the deposits along this coast in depths of from 100 to 300 fathoms are 
the purest glauconitic sands that have hitherto been discovered in existing seas. The 
Challenger collections, and other collections examined by us from different parts of the 
world, have not yielded glauconitic sands so free from admixture with other materials 
as those among the ‘‘ Tuscarora” soundings. The most typical glauconitic sands of the 
Challenger collections contain from 40 to 50 per cent, of Foraminiferous and other 
carbonate of lime shells, together wuth the remains of siliceous organisms. As a rule the 
glauconitic particles in a sample of Green Sand or Mud are not very apparent till after all 
the carbonate of lime shells have been removed by means of dilute acid ; the residue left 
after such treatment is usually of a mottled green or brown colour, and consists of 
numerous dark green grains of glauconite, together with the casts of Foraminifera and 
other calcareous organisms in a paler green, or even brown, colour. This appearance is 
represented in PL XXIV. fig. 1, in the residue of a Green Sand from 150 fathoms, ojff 
the Cape of Good Hope ; and again in fig. 2 of the same plate, in the residue of a 
Green Mud from 410 fathoms, off the coast of Australia. In fig. 3 of the same plate, 
the residue of a Coral Sand is represented, from off the Great Barrier Eeef of Australia, 
near Eaine Island, and it will be observed that in this deposit the residue is for the most 
part made up of the brown-coloured casts of Foraminifera, only a few of them having a 
greenish tint, while typical glauconitic grains are absent. 
The individual grains of glauconite that occur in marine deposits rarely if ever exceed 
1 mm. in diameter, although they may occasionally be agglomerated into nodules cemented 
b57- a phosphatic substance several centimetres in diameter, as represented in PL XX. fig. 1. 
The typical grains are always rounded, often mammillated, hard, black or dark green, 
some of the grains being completely covered with a pale green pellicle ; their surface is 
sometimes dull and sometimes shining. They have occasionally the vague form and 
appearance of Foraminifera and other organisms ; mixed with the typical grains, how- 
ever, as may be seen by reference to the figures on PL XX lY., are numerous pale green 
