242 The American Geologist. April, 1904. 
group vaporization is another limiting stage for some rocks, 
the material of the rock returning to the atmosphere, through 
the agency of the atmosphere (snow, ice). Finally bioclastic 
rocks may be dissolved or vaporized* through the agency of 
organisms (chiefly man), while to a minor degree, the rocks 
destroyed by organisms may also be assimilated. Thus the 
material of the clastic rocks may eventually be returned to the 
atmosphere or the water, or else it may pass into a state of 
fusion. From these states it may then be redeposited by endo- 
genetic agencies. (See diagram 2.) 
In the further subdivision of the clastic rocks, texture or 
size of grain takes precedence over chemical composition, since, 
as has already been noted, the latter is controlled by accident. 
We commonly recognize these sizes of grain, ist that larger 
than what is commonly considered the normal sandgrain, 2d, 
the sand-grain, and 3d, the rock flour or impalpable powder. 
The first texture is most appropriately called rndaceons (from 
nidus, rubble.) The consolidated rock whether conglomerate 
or breccia may be called a rndytc. The term psephyte has been 
used in this sense, for siliceous rocks, but it is a much less 
adaptable one. The second texture, i.e. the sand-grain, is fam- 
iliarly known as arenaceous (from arena, sand), though that 
term is often used also to indicate that the rock in question is 
siliceous. The term arenyte may be used for consolidated 
rocks with this texture, of whatever composition they may be. 
For siliceous rocks of this type the term psammyte has been 
used. The third texture, finally, may be designated by the term 
lutaceous, (from lutum, mud), and for consolidated rocks of 
this type the term lutyte may be used, irrespective of chemical 
composition. Pelyte has been used particularly for argillace- 
ous rocks of this group. 
When a clastic rock is nearly or quite pure in chemical 
composition, as not infrequently happens, we can combine 
chemical and textural terms. Thus a purely siliceous arenyte 
like the St. Peter's sandstone of the Mississippi valley (over 
99 per cent. SiOo) may be called a silicarcntytc, while a pure 
quartz conglomerate or breccia would be a silicirudyte. A 
rock composed wholly of quartz flour would be a pure siHcilu- 
* The best illustration of the ultimate return to the atmosphere either 
wholly or in part of the material of the rocks first rendered clastic bv man, 
may be found in the coal-fires and lime-kilns of the earth. 
