The chemical composition of submarine glauconite is of considerable interest in view of the fact that glauconite is the only silicate which is synthesized at the bottom of the sea, and apparently nowhere else. Numerous analyses of this mineral have been published from time to time, but the results are far from uniform, because the material almost always—certainly in most of the older analyses—was anything but pure. The analysis which inspires most confidence on this score is one which was recently carried out in the Challenger laboratory by Collet and Lee on a purified granular glauconite dredged off the Californian coast by U.S.S. Tuscarora (1879).