Q2 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 qnarry 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 MINERALOaY, LITHOLOGY, AND 

 METALLIFEROUS DEPOSITS. 



By H. C. Salmon, F.G.S. 



The October number of the "Philosophical Magazine" contains a 

 notice, translated from Poggendorff's "Annalen," by Professor 

 GustavRose, on the isomorphism of stannic, silicic, andzirconic 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. 



Zii'conic acid being thus established, and it being sho™ that 

 zircon may be rcgai'ded as isomorphous with cassiterite (the ordinary 



