208 On a Series of Calderite Rocks. [No. 2. 



No. 1 . — Is a common transparent quartz rock, in which on the one 

 side the Iron and Manganese mineral is seen only in small and minute 

 rounded specks like Melanite garnets, as if a little of it in powder had 

 been melted up with the quartz.* Towards the other side of the 

 specimen it is seen to increase in quantity, forming small nests and 

 short veins ; and on the extreme part of it the nests become large, and 

 there are also seen mammillated coatings of the Iron and Manganese 

 upon the quartz. When the mineral is fractured at these nests the 

 Iron and Manganese appears as a brilliant black granular mass. 



No. 2. — In this the quartz is no longer massive, but, like the Manga- 

 nese and Iron, is in coarse grains as if a sort of coarse conglomerate of 

 the minerals had been formed ; on one side this specimen passes into 

 No. 7. 



No. 3. — The coarse grains of No. 2, are here smaller ; the wea- 

 thered surface resembles a granular brown iron ore. 



No. 4. — The granulation is here much finer, and some specimens, if 

 superficially looked at, especially on the weathered surfaces, might pass 

 for a coarse brown and red sandstone. On the fracture it has the 

 appearance of a coarse brownish- white sandstone. 



No. 5. — The sandstone appearance assumes in this variety a resinous 

 glance on the transverse fracture ; and on the horizontal one it becomes 

 laminar and of a reddish-grey, resinous, appearance. The weathered 

 surface glisters like a coarse-grained Diallage or Schiller spar. 



No. 6. — In this specimen the Iron and Manganese appears like a 

 coarse granular black Pitchstone, intermixed with dark brown grains of 

 quartz. The weathered surface is porous and of a dull brick-red colour. 



No. 7. — The granular structure of No. 6 is here much closer and 

 finer. The weathered surface is of a dirty reddish-brown colour. 



No. 8. — The constituents of the mineral are in this specimen so 

 mixed, that they look like a very fine-grained pitchstone-porphyry. 



* It is far more fusible than the quartz, and this accounts for the rounded form 

 of the grains. Yet we should have expected, unless we suppose the quartz to have 

 been an aqueous deposit, that mere igneous fusion would have mixed the materials 

 more completely. Some of the recent discoveries of the solubility of minerals in 

 steam, at merely atmospheric pressures, seem to point to a solution of the singular 

 enigmas which quartz and other rocks so often present when we consider them as 

 produced by mere igneous fusion. 



