Vol. 58. | ANNIVERSARY ADDRESS OF THE PRESIDENT. lxix 
upward until it comes into contact with sea-water containing free 
oxygen. Here the manganese is thrown down, either at the surface 
of the deposit, or on any objects that may be lying exposed on the 
sea-bed. In this way the manganese-nodules so common in certain 
portions of the Clyde sea-area are accounted for. It will be noted 
that the reactions lead to a concentration of the manganese at the 
surface of the deposit, and to a chemical separation of manganese: 
from iron. 
My object in going into these details has been to show that recent 
oceanographical research has greatly enlarged our conceptions of the 
processes involved in the formation of marine sedimentary deposits, 
and that we may look forward to a rapid advance in knowledge 
when these deposits are examined in the same way and by the same 
methods as those to which I have referred. 
But the natural nistory of our sedimentary formations requires. 
for its elucidation, not only a study of the phenomena taking place 
in sea-basins and areas of open drainage, but also of those of desert- 
regions and areas of closed drainage. The recognition of this fact, 
by Ramsay and others between thirty and forty years ago, marks a. 
distinct advance in the evolution of ideas. Our knowledge of the 
phenomena of desert-regions has been greatly increased since 
Ramsay wrote his suggestive papers, by the observations of Blanford, 
O. Fraas, Schweinfurth, Zittel, Richthofen, Walther, and others. 
Dr. Blanford’s paper on the superficial deposits of Persia,* commu- 
nicated to this Society nearly thirty years ago, gives us a vivid 
picture of the essential features of desert-regions. Vast plains of 
fine, pale-coloured, sandy earth, covered in places by shifting sand- 
dunes and often impregnated with salts; gentle slopes of gravel 
and boulders with a surface-inclination of from 1° to 3°, reaching 
upward from the borders of the plains towards the high ground, and 
often attaining a width of from 5 to 10 miles; and broad valleys 
choked with débris debouching on the plains. It is a picture of 
an old, uneven land-surface, which is being slowly buried under 
its own ruins. 
Of late years Prof. Walther has made a special study of desert- 
regions from a geological point of view, and his fascinating book, 
‘Das Gesetz der Wistenbildung,’ based on personal observations. 
in the deserts of Egypt, Arabia, Turkestan, and North America, 
must be read by all those who desire to realize the conditions under 
+ Quart. Journ. Geol. Soc. vol. xxix (1878) p. 498. 
