240 The American Geologist. . Apni, 1904. 
without further rearrangement by wind or water. Perhaps 
the most typical example is to be found in the lateryte, which 
if consolidated without disturbance, would give us a rock in 
which siliceous clay rocks (siliceous argillutytes) are more or 
less admixed with complex coarse fragmentary residual rocks 
(rudytes) of varying composition. As a group of somewhat 
minor rank under this division, rtiust be placed the aeolian or 
anemo clastic rocks already referred to. Here belong the 
aeolian limestones of the Bermudas (anemoclastic calcarentytes) 
and here also belongs the aeolian loess. 
The Hydroclastic group comprises by far the largest num- 
ber of types of clastic rocks. All water-laid deposits of clastic 
material belong here, though the most typical examples are 
such as owe both their clastic condition and their position to 
the waves. Here belong the great classes of stratified con- 
glomerates, sandstones, slates and shales, and here also belong 
the great beds of clastic limestone, resulting either from the 
mechanical erosion and redeposition of growing coral reefs or 
shell deposits, or from the mechanical working-over of older 
limestones. 
While typical hydroclastics are easily recognized, it is ap- 
parent that gradations between this and the other groups exist, 
and that in some cases it becomes a matter of judgment as to 
where a given rock is to be placed. As already noted, the gra- 
dation from pure pyroclastics to pure hydroclastics may be a 
complete one, and the same may be said of the gradations be- 
tween the hydro- and the atmoclastics. 
The Bioclastic group appears at first thought to be repre- 
sented by so small a number of rocks as to be wholly out of 
proportion to the others. But when we add to the rocks broken 
by plants and those ground up by Crustacea or fish on coral 
reefs, the great varieties of rocks for which man is responsible, 
the representation swells out to very noticeable proportions. 
Thus bricks (as material)* plaster, concrete, cement and all 
other rocks which receive their characteristic features through 
man's agency, fall naturally into the system, and thereby into 
their proper relations to all other rocks. Where gravel and 
sand is used in the manufacture of concrete, we have rocks in 
•strictly speaking bricks, when classed as rocks, must be considered as 
aethobalic bioclastics. 
