542 



REPORT 1878. 



Bantry Bay, Kenmave River, and Dingle Bay ; also the mouth of the Shannon, 

 Galway Bay, and Clew Bay. Further north the principal hays and indentations 

 along the line of coast stretching from Broadhaven to Donegal — Killala Bay, Sligo 

 Bay, and Donegal Bay — have heen excavated in their great outlines along lines of 

 strike. 



In conclusion, the author pointed out that nature had adopted the least expen- 

 sive method of working, since it is always easier to excavate along a line of strike 

 than across the tedding. Usually cleavage, or incipient cleavage, is induced along 

 the line of strike hy the forces which upheaved the rocks, and denudation is most 

 easily effected therefore in that direction. 



2. On Hullite, a hitherto ujidescribed Mineral; a Hydrous Silicate of pecu- 

 liar composition, from Carnmoney Hill, Co. Antrim, ivith Analysis. By 

 Edward T. Hardman, F.C.8., H.M. Geological Survey. With Notes 

 on the Microscopic Appearances, by Professor E. Hull, M.A., F.R.8. 



Part I. — This mineral occurs in abundance at Carnmoney Hill, near Belfast, in 

 the basalt forming the old neck of a Miocene volcano. It has never been described 

 or analysed, and has been referred to on the survey maps, and labelled in the survey 

 collection as Obsidian, doubtless from its black colour and waxy lustre. In 

 physical character it somewhat agrees with the Chlorophaeite of Macculloch, but 

 is entirely different in composition, which more resembles that of Delessite. From 

 this, however, it differs essentially in colour, hardness, streak, and specific gravity. 

 It appears, on the whole, to belong to the ferruginous-chlorite group, however. 



Physical characters. — Colour, velvet black. Hardness, about 2. Brittle. 

 Lustre, waxy, dull ; streak olive brown. Before blowpipe, with difficulty fusible 

 at edges to a black glass, which in some specimens is magnetic. Very slightly 

 affected by strong acids, but decomposed when boiled in the powdered state in 

 strong H.Ol. Occurs, filling amygdaloidal cavities in the basalt of Carnmoney 

 Hill, near Belfast, and Shane's Castle, Lough Neagh. 



Chemical composition compared with that of Delessite and Chlorophseite : — 



Silica, SiO., 



Alumina, AL0 3 



Peroxide of Iron, Fe.,0., 



Protoxide of Iron, FeO 



Protoxide of Manganese, MnO. 



Lime, CaO 



Magnesia, MgO 



Water, II 2 



Carbonic Acid, C0. 2 



Formula, WJL"\®fi a + 7H,0 

 Sp. gr 



Hullite 



39-437 



10-350 



20-720 



3-699 



trace 

 4-484 

 7-474 

 13-618 

 traces 



99-782 



1-76 



Delessite* 



31-07 



15-47 



17-54 



4-07 



19-14 



0-46 



11-55 



100-00 



2-89 



Chlorophceitef 



33-30 

 26-70 



40-00 



100-00 



FeSi0 3 + 6H,0 

 2-02 



It will be noticed that there are striking differences in the composition of the 

 new mineral from the others. The large amount of water in Chlorophseite, and the 

 fact that it appears to have been obtained by difference, seems to throw some 

 doubt on the analysis. 



It is difficult to express the composition of Hullite by a chemical formula. 



* Dana's, ' System of Mineralogy,' 1874, p. 497. 



-j- lb. p. 410. Also Western Isles of Scotland. John Macculloch, M.D., p. 



50.-,. 



