Mr. E. T. Harpman—On the Chemical Composition of Chert. 91 
Anatysis XI. 
Total 
’ oe b. Analysis. 
Si0, (insoluble), : : : ~ » 95°50 95°50 
SiO, (soluble), : . : trace - - 
Fe,0,, : ‘ ‘ - 0:10 0:10 
A1,O,, . : : d - 1:95 1:95 
FeO, : ; : A - 0:15 0-15 
MgO, : : : - trace trace 
CaCO,, 6 6 4 : 0:87 - 0:87 
CaSO, : 6 c 5 trace = trace 
Na,O, : : , ; trace = trace 
Water and organic matter, . : 1-43 - 1-43 
Insoluble residue, ; ‘ ; 97:60 = - 
99:90 97:70 100-00 
Specific gravity, 2°614. 
It is curious that the chemical composition of this specimen is almost identical 
with that of No. 12, which is taken from the same horizon, but at a distance of 
some miles.” 
No. 15, A very hard white chert, very fossiliferous, passing into a gray siliceous 
limestone—effervesces slightly. 
ANALYsIS XII. 
Total 
: Analysis. 
SiO, (insoluble), ; 4 ‘ _ 90:90 90:90 
Si0, (soluble in HCl), : : trace = trace 
Fe,0O,, ; : ‘ : 0:40 0:30 0:70 
A1,O,, y ; : ; 0:70 0:65 1-35 
FeO, : ; : ; 0:30 ~ 0:30 
CaO, , ; ‘ A - 0-50 0:50 
MgO, - trace trace 
CaCO,, ‘ : : 5:90 — 5:90 
MgCoO,, . : : : 0:25 = 0:25 
Water, : : 0:35 = 0-35 
Insoluble residue, . b : 92-15 = ma 
100-05 92°35 100-25 
SiO, soluble in caustic potash, 0°50 per cent. 
Specific gravity, 2:698. 
The chert presented the same anomalous behaviour already noticed in No. 10. 
That is, that after having been fused with the alkaline carbonates and dissolved in 
water, no silica was precipitated on addition of hydrochloric acid, and the solution 
remained perfectly clear, until evaporated down nearly to dryness. In all the 
other analysis the silica was immediately thrown down on the addition of acid, and 
I am unable to account for these exceptional cases, otherwise than on the supposition 
that the cherts must have undergone some degree of alteration. What makes this 
case more remarkable is, that boiled with a strong solution of caustic potash, these 
specimens yielded hardly any silica as may be seen from the analysis. 
In this connexion I should note the fact, that none of the cherts yield more than 
* These cherts are also on the same horizon as that near Carlow, which is the Irish locality for Lydian- 
stone given by Greg and Lettsom in the Manual of Mineralogy of Great Britain and Ireland, p. 91, 
