12 Transactions, 



Quarry, " there is no line of demai'kation to be drawn between 

 the higher and lower parts o£ the rock ; they cannot indeed be 

 discriminated except by actual fracture and inspection, the whole 

 mass appearing as one and indivisable." A striking instajice of 

 this metamorphic change lately came under my observation at 

 the Black Craig Mine, near Newton-Stewart. I observed in the 

 rubbish heap considerable quantities of a dark greenish black 

 rock, which had been thrown out of the mines. On examination 

 I found it of a very soft nature, readily disintegrated by exposure 

 to the atmosphere, easily cut with a knife, and some portions of 

 it containing amygdaloidal cavities filled with calcite. It was 

 too soft for serpentine, but evidently of a serpentine nature. On 

 asking the superintendent of the mine about it he said there was 

 a vertical band of this rock running through the workings from 

 6 to 12 feet thick, the direction of the band being about N.E. to 

 S.W., which exactly coiresponds with the strike of the trap dyke 

 running through the country, as is shown in the geological maps 

 recently published. It immediately struck me this might be an 

 instance of a transformed trap dyke such as Professor Geikie 

 alludes to in his paper. I sent him some specimens. The rock 

 is so soft that he found it extremely difficult to obtain satisfactory 

 slices for microscopic examination. He says — " In the meantime 

 I can announce with certitude that it is an altered eruption 

 plagioclase rock or trap, the felspar and magnetite ore quite 

 distinct, but the magnesian silicate, whatever it was, has gone. 

 It is not a serpentine in the proper sense, but rather a ser- 

 pentinized diabase or basaltic rock." The whole of the mass in 

 question appears to have been completely transformed. I noticed 

 nothing amongst the large quantities I examined that had the 

 least approach to a hard trap or basalt. I found no appearance 

 of any trap or dyke appearing on the surface in the neighbour- 

 hood. From its extreme tendency to weather and crumble down, 

 any part of the eruption, if it ever came to the surface, must 

 have disappeared ages ago. The external mineralogical charac- 

 teristics of the rock are — Hardness, 2-5; specific gravity, 2-66; 

 colour, dark greenish black ; texture, gi-anular ; streak, light grey. 

 Specimens of this rock and a sketch of a microscopic section sent 

 by Mr Dudgeon were handed round amongst the members and 

 examined with much interest. 



Elfin Pipes. — A paper by Mr "W. G. Gibson, entitled " Elfin 



