162 Proceedings of the Royal Irish Academy. 



that miEeral by Macculloch and Forcliainmer, -which give very 

 extraordinary results. The presence of so called chlorophseite ha&^ 

 heen noted by Portlock^ as occurring in the basalt of Down Hill 

 (p. 227) ; Magilligan — abundantly in several beds exposed in the 

 section there (p. 152-3), and at Carrick-a-rede, where the mineral 

 imparts a porphyritic appearance to the rock (also at Craigahulliar, 

 p. 154), and he mentions localities as Crosseagh and south Eallylagan 

 where the trap, wanting the imbedded chlorophaeite, has cavities occa- 

 sionally lined with obsidian (p. 155) — this he mentions as occurring* 

 at the Giants' Causeway. !Now it seems improbable that a highly 

 acidic mineral such as obsidian would be found in basalt; and I am. 

 inclined to suppose that Portlock, as Mr. Du JN'oyer did afterwards,, 

 mistook the Carnmoney Hill mineral for obsidian. 



"Whether this Carnmoney Hill mineral is the same as that which 

 Portlock calls chlorophseite I cannot say, as I have not seen specimens- 

 from the localities he names. But it is not at all clear that Portlock's 

 so called chlorophseite is that of Macculloch, since analyses of it are 

 wanting. If it be the same mineral as that I have examined, the- 

 composition is entirely different. 



In chemical composition the mineral approaches more nearly to 

 delessite. However, there are still very important differences, as will 

 be seen on comparison. Delessite contains considerably less silica, 

 more alumina, and more protoxides — lime especially being abun- 

 dant. Again, the physical characters do not agree, — delessite is 

 harder ; its gravity is nearly f more, its colour and streak different, — 

 so that on the whole we must regard this mineral as a new one^ 

 although possibly belonging to the ferrugenous chlorite group. 



Method of Analysis. — Separation of the mineral. This is so im- 

 portant a point that it may be well to devote a few lines to the de- 

 scription of the manner adopted. Although the mineral occurs most 

 abundantly in very small nodules, it was found, to be a most tedious 

 process to extract sufficient of it even for a qualitative analysis. One 

 method was to crush the rock — extract as much of the matrix as pos- 

 sible by means of a strong magnet, the small particles of magnetite, 

 or perhaps native iron disseminated throughout it, rendering this pos- 

 sible, and collecting the mineral bit by bit with a forceps from the 

 felspar and augite which remained behind. This, however, promised 

 to be an endless proceeding — but I fortunately at the time happened to 

 meet with a notice of the use of Sonstadt's solution for that purpose ; * 

 this I tried, and it succeeded so admirably that, although I have already 

 noticed the result elsewhere,^ a short description of the process may 

 not be out of place here, as it is a matter that cannot be too well known 

 to mineralogists. 



1 Geological Heport on Londmidcrry , Antrim, §c. 

 - Prof. Church, English Mechanic, January, 1878. 



■^ "On the applicability of Sonstadt's solution to the separation of minerals for 

 chemical analyses." — C'hciuUal J\'cwx, April, 1878. 



