400 Scientific Proceedings, Royal Dublin Society. 



METHYLOTIC ROCKS, or SERPENTINES. 



The name Serpentine is more applicable to the methylotic lime- 

 stones than to the methylotic volcanic rocks. We will, however, 

 here use it in the broad popular sense, and include under it all the 

 methylotic limestones and volcanic rocks, also the rocks allied thereto- 

 Of late years Lithologists have greatly subdivided these rocks, the 

 principal subdivisions of the former being called ophiolytes, ophi- 

 calcytes, and ophidolomytes ; and of the latter, ophyte and eklogyte, 

 with the allied rocks steatyte (soap-stone) and pyrophyllyte (cam- 

 done). 



Dana divides the massive Serpentine or ophyte into precious 

 Serpentine of a lich old green colour, of pale or dark shades, and 

 translucent, even when in thick pieces ; and common Serpentine of 

 dark shades of colour, and subtranslucent. The latter is hard 

 and difficult to work on account of impurities. Many statues 

 however, in Egypt and India are made of rocks of this class. Eklo- 

 gyte is still commonly called Serpentine. Formerly steatite and 

 pyrophyllyte were also thus classed; now many separate them. 

 Steatyte and pyrophyllyte are still confounded together by most 

 people, their appearance being very similar ; yet they are chemi- 

 cally very distinct, the former being a silicate of magnesia, and 

 the latter a silicate of alumina. Steatyte seems to be always an 

 adjunct of volcanic rocks, while the other occurs in general as a 

 bedded rock : steatyte, however, may occur as " fault rock," if the 

 latter had been made up of volcanic rock debris or volcanic tuff. 



METHYLOTIC LIMESTONES and DOLOMYTES. 

 OPHIOLYTES, OPHICALCYTES, and OPHIDOLOIIYTES. 



The rocks of this division now of commercial value are recorded 

 only in the west of the Co. Galway, and are known as Connemara 

 greens. They have indeed been found also in the counties Donegal 

 and Waterford, but from neither of these counties do any stones 

 come into the market, while the beds or veins seem to be so limited 

 in extent that there does not appear much prospect of their ever 

 doing so. 



