346 [B.N.F.C. 



On the whole, I feel convinced that such deposits of 

 chalcedony in volcanic lavas, and this one at Carnmoney in 

 particular, are contemporaneous formations of the rock, and 

 that they were formed during the last stages of the lava's cool- 

 ing and drying. Furthermore, I am, constrained to believe that 

 the zeolitic or calcitic layer, and the siliceous contents of these 

 veins and cavities, owe their origin, not to' the decomposition of 

 the mother-rock, but to the final process of its construction. In 

 all probability the water present in the hot lava pjayed an 

 important part in the formation of these minerals. We may 

 look upon this process of vein-filling in lavas as an example of 

 the thorough economy so often exhibited in Nature. During 

 the consolidation of the lava contraction took place, and the 

 cracks or veins were formed. These were points of weakness 

 in the rock — real wounds — and Nature immediately set about 

 their healing. The residual magma — the very life-blood of the 

 lava we might call it — was secreted into- these rents, impelled 

 more or less by physical forces, but, nevertheless, continually 

 guided within itself by active crystalline energy. The hullite, 

 calcite, zeolites, and chalcedony were deposited each in its 

 order, and when the rock was cold and dry these minerals stood 

 each in its place, and each ready to play its own part as a 

 necessary portion of the solid earth. There is an unbroken 

 sequence in the mineral matter from the main constituents of 

 the lava to» the chalcedony in the centre of the veins. Professor 

 Cole has shewn that the hullite plays the part of a true ground- 

 mass in the intercrystalline spaces of the rock. Lacroix ob- 

 served that the hullite has included in its formation minute 

 crystals of felspar and magnetite ; also small crystals of calcite. 

 The calcite and zeolites follow upon the hullite 1 , and finally the 

 chalcedony, which in its growth has included crystals of calcite 1 , 

 and zeolitic matter. 



7. That the calcitic or zeolitic layer of the veins is often 

 much weathered I have already mentioned, and very often its 

 former presence can only be inferred from the hollow pseudo^ 

 morphous cavities in the chalcedony. This calcite has in some 

 cases been re-deposited in other portions of the veins, and 



