Classification of Sedimentary Rocks. — Grabau. 243 
tytc. Again, a pure limestone conglomerate or breccia, is a 
calcirudyte* a lime sandstone like that of the Bermudas (ane- 
moclastic) or like the great beds of Palaeozoic clastic lime-sand- 
rocks of the middle west (hydroclastic) are calcarenytes, while 
rocks made up of lime-flour like many beds in the Palaeozoics, 
and the lithographic stone, are pure calcilutytcs. Waterlimes 
are siliceous or argillaceous calcilutytes as the case may be. 
Clay rocks, whether pure or impure, are generally known 
by the structural terms shales or slates. They are always 
lutytes, and when pure may be called by the name argillutyte. 
Most generally shales or slates are more or less siliceous or cal- 
careous argillutytes, or they may be highly carbonaceous argil- 
lutytes, in which case they are known by the misleading term 
"pyroschists." Rudytes in which argillaceous material pre- 
dominates either in the fragments or in the cement, are not 
unknown, but pure argillirudytes are probably represented only 
by local examples. 
The three types of composition mentioned above cover the 
most important cases. Impure types bridge the chasms be- 
tween the pure types. Thus, besides those mentioned, there are 
calcareous, argillaceous or ferruginous silicarenytes and sili- 
cilutytes, and likewise argillaceous, siliceous and carbonaceous 
calcarenytes and calcilutytes. Besides, there are micaceous feld- 
spatic or glauconitic silicarenytes, and micaceous calcarenytes. 
Strongly feldspatic arenytes or arkoses and glauconitic aren- 
ytes or green-sand rocks are further modifications of the types. 
Finally there may be in disturbed iron or coal regions auto- 
clastic ferrirudytes, or carborudytes, (iron breccias or coal 
breccias) or even ferrarenytes and ferrilutytes, or carbarenytes 
and carbolutytes. All these, however, will be represented by, 
local examples only. 
The divisions made in the endogenetic group, into original 
and metamorphic, may also be carried out in the exogenetic 
group. "We may, however, substitute here the terms unconsol- 
idated and consolidated for original, and for the early stages of 
diagenism. The solidification or lithification of clastic rocks 
by chemical means, is clearly a process of diagenic action, but 
diagenism does not stop here, there being numerous changes 
which a clastic rock may suflFer after solidification, which are 
• Grabau. BuU. Geol. Soc. Amer., vol. xiv, p. 349. 
