384 
THE VOYAGE OF H.M.S. CHALLENGER. 
particles belonging to the ancient or continental rocks in the residue after the removal of 
the carbonate of lime. In like manner, when glauconite is found in a Red Clay or 
Diatom Ooze, traces of continental debris can always be detected during the microscopical 
examination of the mineral constituents. The Red Clays, for instance, off the west coast 
of Africa and the coast of Australia, and towards the polar regions, contain apparently 
wind-borne or ice-borne particles of quartz, orthoclase, white mica, epidote, zircon, and 
fragments of gneissic and granitic rocks ; and it may be urged either that the glauconite 
has been transported to these deposits at the same time or has been formed in consequence 
of the association with the above minerals. The view that it has been formed in situ 
is probably the correct one, for we have seen that it is thus formed in shallower water 
deposits like the Green Sands, where its associations are much more distinctly marked 
and its progressive development more easily traced. Finally, we may again point out 
that glauconite is now being formed in those marine deposits in more or less close 
proximity to continental shores, where the debris of ancient rocks makes up a large part 
of the deposit, and especially in those regions where this debris has been for a long 
time exposed to the action of sea-water, and has consequently undergone profound 
alteration. 
When describing the Red Muds off the coast of Brazil, it was stated that glauconite 
and glauconitic casts appear to be completely absent from these deposits. These Red 
hluds differ from the vast majority of terrigenous deposits in the large quantity of 
ochreous materials borne to these regions by the rivers of South America. In the 
deposits in the Yellow Sea glauconite would also seem to be absent from similar Red 
^luds. In these positions all the conditions for the formation of glauconite are, so far as 
we can judge, present, with the exception that the iron is all in a higher state of oxidation 
than in the Green and Blue Muds ; but in what way this can prevent the formation of 
glauconite is difficult to explain satisfactorily. 
Geological Distnhution . — The geographical and bathymetrical distribution, as well as 
the mineralogical associations of glauconite above pointed out, become especially interest- 
ing and instructive when we recall the analogies which they present to what has taken 
place in past geological times. It has already been stated that glauconite is one of the 
minerals most widely distributed in sedimentary rocks. It is found in the primary 
formations of Russia and Sweden among sands and gravels, in the Cambrian sandstone 
of North America, in the Quebec group of Canada, and in the coarse Silurian sands of 
Boliemia. In the secondary formations its presence is more pronounced — for example, 
ill tlie Lias, and especially in the middle and upper layers of the Jurassic system in 
Russia, in Franconia, in Suabia, and in England. It has a still greater development in 
the sands, marls, and chalks of the Cretaceous formation; it will suffice to recall the 
glauconitic rocks of tlie Neocomian, of the Gault, and of the Cenomanian in various 
regions, sucli as the glauconitic marls of France, Germany, England, and several parts of 
