346 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1914. 
been a particularly active cause of changes in the course of ocean 
currents and consequently of similar destructions. 
This is one of the reasons, as I have elsewhere stated, why each 
great period of folding has been followed by a phase of phosphatic 
deposition, just as we find after it, from somewhat different though 
mutual causes, oil-bearing hydrocarbon deposits, saline deposits, and 
deposits of iron. 
If we revert to the phosphates, the greatest concretion which has 
been, dredged up came from Agulhas Bank, where there are some 
genuine greensands (glauconitic) in the phosphates similar to those 
of the upper Cretaceous; it measured 23 by 16 by 12 centimeters. 
Oftener these nodules, like those found in geologic strata, as in the 
Gault or the Liassic, are less than 10 centimeters. Their form is 
similar, being irregular, the contours at times rounded, sometimes 
angular and with an outer deposit which is at times dark and shiny 
when the phosphate existed in the ooze, at other times gray and dull 
when this phosphate leaving the ooze was covered over with organ- 
isms, such as bryozoans, corals, sponges, and foraminifera. The 
nodule itself is often covered with shells of lamellibranchs, brachio- 
pods, and gasteropods, more or less completely phosphatized, as so 
often occurs with geologic phosphates; we also find in it particles of 
calcite, of glauconite, and of detrital minerals. The relative propor- 
tion of shells fixes the relative amount of carbonate of lime it contains. 
Finally, you observe, in these present phosphatic nodules, a fact 
which is constant in the geologic strata; that is, the transition into true 
iron ores through the medium of the glauconite. The nodules are 
often yellowed or browned by peroxide of iron due to a decomposi- 
tion of the glauconite like that which we shall see taking place in the 
formation of true iron ores, and, like that, curiously similar to the 
phenomena produced in the superficial continental reactions above 
the hydrostatic level, in what is called the zone of peroxidation. 
Potash, a soluble element which plays an important réle in glauconite, 
is eliminated as it may become exposed and that is why the iron is 
peroxidized. 
This is a case of what I have above called diagenesis; but other 
cases exist which apply more directly to the phosphates. In a 
chalky ooze of phosphatic elements, one can readily ascertain that the 
phosphate is gradually concentrated and concreted around nuclei 
already phosphatized, like that produced in the growth of all crystals, 
or likewise by pseudomorphism, on some simple calcareous elements. 
This concentration began beneath the sea—it is diagenesis; it continued 
by metasomatosis after the emergence of the phosphates to their 
present levels, and it has thus played an enormous role in the for- 
mation of utilizable lodes as they are presented to us. The soluble 
phosphate which appears to be at first in the state of phosphate of 
