ld 
Mr. E. T. Harpman—On the Chemical Composition of Chert. 87 
be sections of these sulphates; the common crystalline form of which cut vertically 
through the brachydiagonal would show a six-sided figure.* 
No. 4. Black chert with corals highly silicified, extremely hard; cannot be 
scratched, does not effervesce with acids, parts of the corals replaced by crystalline 
silica. 
Anatysis III. 
a b. Total 
Analysis. 
Si0, (insoluble), 5 : : - 91°645 91-645 
SiO, (soluble), 5 } : 1-500 - 1:500 
Be,0;, 0-650 0-740 1-390 
Al,O,, , : : : 
CaO, : : ‘ : - 0665 0:665 
MgO, 4 : : 3 _ 0-090 0-090 
CaCoO,, 6 6 : ; 3150 - 3150 
MgCO,, : : ; : 0-500 - 0:500 
Water and organic matter, . : 0-800 - 0-800 
Insoluble residue, . ; ; 930°50 _ — 
99-650 93-140 99-740 
Specific gravity, 2°769. 
No. 5. A dark siliceous limestone passing into Black Chert. The limestone 
scratches easily and effervesces freely, but these characteristics diminish as the 
cherty parts are reached. The knife makes no impression on these, but they 
effervesce somewhat freely. 
Anatysis IV. 
Total 
a b- Analysis. 
SiO, (insoluble), 2 : ¢ - 8:40 8-40 
Fe,0,, 7 of ‘6 
ator \ paeanteg 1-70 0:50 2:20 
FeO, : 6 : : 0-70 - 0:70 
CaSO, é 4 4 j 82°50 = 82-50 
MegCoO,, : : Q 9 1:00 = 1:00 
Water, organic matter, and sulphur, . 4°85 = 4:85 
Insoluble residue, A 5 : 8.99 = = 
99°74 8:90 99°65 
Specific gravity, 2°649. 
That the microscopic characters of this and specimen No. 9, so much resemble 
those of the true chert, is a point in favour of the pseudomorphic character of the 
latter. 
No. 7. Dark chert, extremely hard and dense. In ordinary condition cannot be 
scratched ; effervesces rather freely with acid, and the places touched with acid can 
be afterwards scratched. Gives off a very fetid odour (sulphuretted hydrogen 
from the remaining organic matter, or probably due in part to the presence of 
sulphide of calcium) on being broken up. 
*M. Dieculafait finds that strontium is widely and appreciably diffused in sea and spring waters ; also 
in marine rocks, minerals, and fossils. (Comptes Rendu, lxxxiy. 1303.) 
Q 
