52 Th' American Geologist. Jan. 1891 
near by, whose bowl is now empty and dry, was found to consist 
of the same moss sinter. 
Upon burning off the organic matter of the green and living 
moss the structure remains, formed of Fe,,0 3 , so that the iron 
reall}* forms part of the plant tissue. An analysis of this ma- 
terial made in the U. S. Geol. Survey Laboratory shows it to have 
the following composition : 
SiO a 1.37 
Fo,b :j • 63.03 
S0 3 8.35 
AlJo 3 0.08 
Water and organic matter 26.94 
Total 09.77 per cent. 
In this case the iron has probably been in solution as ferrous 
sulphate which has been oxidized with the formation of the ferric 
oxide and sulphuric acid. 
Although the extraction of silica to build up plant tissues is not 
confined to the lower orders of plants, it is only in the alga? and 
mosses that this property is so highly developed as to form min- 
eral deposits. The extraction of silica from sea-water has long 
been recognized as one of the peculiar and as yet unexplained 
properties of the microscopic, plants called diatoms. The well 
known and constant association of amorphous silica and organic 
matter cannot be accepted as explaining this secretion of silica by 
diatoms since it is manifestly a result of life or vital agency. It is 
perhaps unnecessary to call attention to the great thickness of the 
beds of nearly pure silica, composed of the remains of diatoms, 
which are found in all parts of the world. The largest deposits 
are undoubtedly those in Nevada, described by Mr. Arnold Hague 
in the reports or the 40th Par. Survey as being several hundred feet 
thick.* At the present day diatoms have a widespread distribu- 
tion in both salt and fresh water and are forming siliceous strata 
by the accumulation of their remains, on the bottom of the ocean 
and also in lakes, ponds and bogs on the land. 
In the geyser basins of the Yellowstone park, there are beds 
several feet thick and square miles in extent, which consist of the 
♦Reports, 40th Parallel. Vol. ii. 
