xvi PROCEEDINGS OF THE GEOLOGICAL socieTY. [May 1902, 
notable exceptions to the general statement that I have just made. I 
may refer, for example, to the important paper by Gunnar Andersson 
on the Cambrian and Silurian phosphatic rocks of Sweden, to 
which I have directed attention in another place, and to the work 
of Cayeux, William Hill, and Hume on the French and English 
Chalk. 
But, after all, it is to the increase in our knowledge of the sedi- 
ments now in course of formation in depressions and hollows of the 
lithosphere, that the evolution of ideas is mainly to be attributed. 
So long as geologists were acquainted only with the deposits forming 
along sea-margins and in areas of open drainage, they were in- 
sufficiently supplied with the data necessary to enable them to 
investigate the natural history of many stratified deposits. Geo- 
graphical and oceanographical exploration during the latter half of 
the century have greatly enlarged our conceptions, and given 
precision and definiteness to ideas that must otherwise have remained 
vague and uncertain. 
We now know that ocean-basins and desert-regions are the 
principal areas of deposition, and that the rocks which are forming 
in both these areas have their geological representatives. Ocean- 
basins form the ultimate receptacle for the mechanical detritus 
washed down by rivers from areas of open drainage. This detritus, 
together with that worn from the coast-lines, is distributed by waves, 
tides, and currents along the margins of the continents in such a 
way that the coarser deposits are laid down near the shores, and the 
finer deposits out atsea. A narrow zone of shingle spreads along the 
shore, then a broader zone of sand, and, finally, a still broader zone 
of mud, generally blue, but sometimes red, where tropical rivers. 
supply the sediments from regions in which the surface-weathering 
is of the lateritic type. The mechanical sediments shade into the 
organic, and these again into the abyssal red clays. Areas of open 
drainage have, as a rule, a moist climate, and the mechanical 
sediments deposited in the open ocean therefore represent the more 
or less insoluble residues of the crystalline rocks, and consist 
largely of such substances as quartz, mica, zircon, rutile, ilmenite, 
eyanite, hydrated aluminous silicates, and the oxides of iron and 
manganese. The soluble constituents—lime, magnesia, and the 
alkalies—may be carried to an indefinite distance from the land, 
and can only be separated by organic or chemical agencies. 
Organisms are abundant, and their hard parts are often preserved 
in the deposits ; moreover, the presence of organic matter exercises 
