STATE GEOLOGIST. U8 
Per cents. 
Silicate gartete teen OMe Ni hott Macs Scan cailya Peps take shit, netat 58.38 
PNRITO TUTE Stoney ea ce eR oA cs a eau aR = SS 20.89 
JENST TAG ODIO V2 CNET SS tah oe eR ai ir na AE a es ea Ne thes) 
BIN eee eG ene reno me eS ue ha Mak ately gua 0.44 
Miatoiveslawenmr es coe metenep ie eat etree eer d GNDoL Oe Gt Ayah 1.57 
HO Gers Lae erry er cnet ete neta cerned Voter, gee Sena ear be a 4.78 
RSLOKG Ke Hes (att Zel iby esratl aaty en eet I Stn aR GR nD an AUT ee dc 0.34 
(CWE OXG TOYS Sez Baa tet ees i Bt tae tan Deak a eat a yA 
@hemicalawatercsetehmnn a aany st es eee tae eee 4.82 
In another sample of this shale there was found an iron content of 
10.67 per cent. (as ferric oxide), of which 7.96 per cent. was ferrous iron, 
reported as ferrous oxide. The same shale was likewise found to contain 
1.63 per cent. of sulphuric anhydride (SO,) soluble in water. 
From this the inference must be drawn that the material is liable 
to be too high in sulphur to be used as a satisfactory cement material. 
But that does not mean that this is true of all the shales; this point 
must be determined for every particular locality where this shale is found. 
Plastic, Ferruginous Clays, Brick Clays, Weathered Shales.—As 
the shales succumb to the influence of the atmospheric agencies they 
gradually lose their shale structure and become again clays, with of 
course the same chemical composition, except that all oxidizable sub- 
stances are converted into the higher oxygen compounds. Ferrous car- 
bonate is decomposed and becomes ferric oxide, iron pyrites is changed 
to ferric sulphate. As a result we have in place of the hard mass show- 
ing a pronounced parallel structure a soft clay, possessing a much greater 
plasticity than did the shale. On the surface and outcrop of every shale 
deposit, we find, hence, plastic clay, and if the shale is suitable for cement- 
making by virtue of its chemical composition and fineness of grain the 
clay derived from it is much more valuable, since its softness renders 
it so easy and cheap to grind. In addition to this comes the uniformity 
of the composition, a property peculiar to shales, so that a shale clay is 
apt to be a material of magnificent working qualities. 
Alluvial Clays——As we have already seen, the clayey and sandy 
materials carried along by a stream are deposited according to their 
size and specific gravity dependent on the velocity. The swifter the 
stream flows the coarser will be the matter deposited by it. We call 
the comparatively fine rock matter deposited by a river alluvium. 
Usually the rivers flow through a narrow plain within which the 
stream winds from side to side and over which the water spreads in 
times of flood. The larger the river the wider will be this plain. At 
the same time the river erodes for itself a deeper and deeper bed, so that 
extensive banks and terraces are formed on both sides of the stream. 
The character of an alluvial clay is hence largely dependent upon 
whether the stream was flowing rapidly or slowly, whether it was a large 
or small, deep or shallow river, whether the course was straight or 
crooked. From this it follows that in looking for a suitable alluvial clay 
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