62 
THE GEOLOGIST. 
With one or two exceptions, the whole of the corals I have here 
attempted to describe may be found within the limits of an hour 
spent in any quarry of Wenlock shale, or limestone. The few I have 
omitted to mention have but slight points of difference, and are ac- 
counted rare ; but from a glance at this, every reader or collector 
will acknowledge that the coral-polyp held no mean place among the 
workmen of old. 
CURRENT NOTES ON MINERALOGY, LITHOLOGY, AND 
METALLIFEROUS DEPOSITS. 
By H. C. Salmon, F.G.S. 
The October number of the "Philosophical Magazine" contains a 
notice, translated from PoggendorflF's "Annalen," by Professor 
Gustav Rose, on the isomorphism of stannic, silicic, and zirconic acids. 
Stannic acid (Sn) forms the mineral Gassiterite, silicic acid (Si) is 
Quartz, zirconic acid, which Rose considers to be Zr, has hitherto 
been classed as an earth or oxide, as zirconia, with composition Zr, 
or Zr. The mineral zircon, hitherto held to be a silicate of zirconia, 
must now, according to this, be merely considered as an isomorphous 
compound of one atom of zirconic acid and one atom of silicic acid 
(Zr + Si) . This mineral species has always been remarkable for the 
variation of hardness and gravity in specimens from different local- 
ities, which according to this hypothesis may be accounted for by the 
unequal proportions of the two acids ; the heavier and harder speci- 
mens containing the more zirconic acid, whose equivalent would be 
481"20 compared with 384'888 that of silica. In the case of a variety 
found in Russia by Hermann, composed of two atoms of Zr, with 
three atoms of Si (Zr^ Si^), the specific gravity was only 4'06, while 
that of the mineral of the ordinary composition varies from 4'5 to 4'8. 
Zirconic acid being thus established, and it being shown that 
zircon may be regarded as isomorphous with cassiterite (the ordinary 
