68 ANNUAL REPORT 
white or very light-colored cement. Such rocks would be the pegmatites, 
similar to Cornish stone, used so extensively in the pottery industry ; be- 
sides being low in iron, they are also low in alumina and high in silica, 
which would produce, if properly made, a safe cement, slow-setting, with- 
out the use of plaster. This question deserves more practical attention 
than it has yet received. | 
Classification of Clays—It will not be found advisable to attempt a_ 
classification going into all the variations of clayey materials; for the pur- 
pose of the cement manufacture a less complicated system will suffice. : 
( White or light colored rock-ageregate. Kaolins. 
A. Primary : 
Clayisee 
| Ferruginous hydrous rock-aggregate. 
( Plastic kaolin 
High grade clays. 
( Fire clays....< Flint clays. 
| Low grade fire clays. 
| ( Aluminous. 
Ferruginous. 
Shales....... <{ Silicious. 
| Calcareous. 
B. Sedimen- i 
tay Clays } | Carboniferous. 
| 3 
Plastic _ { Weathered shale 
Herruginous | 
or Calcareous 4 Deposited in swift running water 
clays 
GstUI Rave Eos trie oiokecis bs { Deposited in slow running waters 
| | Deposited in still water. 
Drift clay proper. 
L Glacial resect: 
Re-deposited glacial clay. 
J. Light Colored Rock Agegregate.—When igneous rocks of the 
granitic type break down under the influence of the weathering agencies, 
the transition from the feldspathic minerals and other aluminum silicates 
to hydrous kaolinitic substances is not sudden, but gradual. On top of a 
decomposing layer of granite we would have the finest grained clavey 
material, while on approaching the mother rock the rock found wouid 
bear more and more the character of the granite. Fragments of the old 
rock would be found surrounded by the more or less completely hydrated 
material. 
If conditions happen to be such that the clay (kaolin) is obtained 
solely from the feldspathic rocks without admixture of augitic minerals 
or hornblende, the resulting material will be composed of clay substance 
( Al,O,2SiO,2H,O), more or less decomposed grains and fragments of 
