of Edinburgh, Session 1883-84. 
511 
tinge. Lapilli, pumice, and glassy fragments, often altered into 
palagonite, seem always to be present, and are frequently very 
abundant. The mineral particles are generally angular, and rarely 
exceed 0*08 mm. in diameter; monoclinic and triclinic felspars, 
augite, olivine, hornblende, and magnetite are the most frequent. 
When quartz is present, it is in the form of minute, rounded, 
probably wind-borne grains, often partially covered with oxide of 
iron. More rarely we have white and black mica, bronzite, actino- 
lite, chromite, glauconite, and cosmic dust. Siliceous organisms are 
probably never absent, sometimes forming 20 per cent, of the deposit, 
at other times they are only recognisable after careful microscopic 
examination. In some regions the frustules of Diatoms predomi- 
nate, in others the skeletons of Radiolarians. 
The fine washings, viewed with the microscope, are not homo- 
geneous. The greater part consists of argillaceous matter coloured by 
the oxides of iron and manganese. Mixed with this, we distinguish 
fragments of minerals with a diameter less than 0'05 mm., and 
minute particles of pumice can nearly always be detected. Frag- 
ments of Eadiolarians, Diatoms, and siliceous spicules can always 
be recognised, and are sometimes very abundant. 
Pteropod Ooze . — This deposit differs in no way from a Globigerina 
ooze except in the presence of a greater number and variety of 
pelagic organisms, and especially in the presence of Pteropod and 
Heteropod shells, such as Diacria, Atlanta, Styliola, Carinaria, &c., 
&c. The shells of the more delicate species of pelagic Foraniinifera 
and young shells are also more abundant in these deposits than in a 
Globigerina ooze. It must be remembered that the name “ Pteropod 
ooze ” is not intended to indicate that the deposit is chiefly composed 
of the shells of these molluscs, but, as their presence in a deposit is 
characteristic and has an important bearing on geographical and 
bathymetrical distribution, we think it desirable to emphasise the 
presence of these shells in any great abundance. It may here be 
pointed out that there is a very considerable difference between a 
Globigerina ooze, or a Pteropod ooze situated near continental shores, 
and deposits bearing the same names situated towards the centres 
of oceanic areas, both with respect to mineral particles and remains 
of organisms. 
Diatom Ooze . — This ooze is of a pale straw colour, and is composed 
