110 Proceedings of the Eoyal IriaJi Academy. 



or Hipidolife-schist, Tolcyte, or Talcschisf, Fehityte, or Felsite-schist, 

 Sclmtose-Lirnestone, ScJiistose-dohmyte, Ophiohjte, or Serpentine, and 

 Steatyte. 



Aryilhjte. — Typical argillyte is an argillous rock, in Trhich. the 

 planes of lamination are more or less glazed, and also often the planes 

 of cleavage, hut not always, as some slates helonging to the meta- 

 morphic series have a more or less earthy cleaYage sui-face. The most 

 common of the varieties in this area seems to he CMoritic-ary illyte, 

 Clay-slate, Steatitic-argiUyte, some of Tvhich might he called Stea- 

 tityte, or Steatite-schist, Sornhlendic-ary illyte, Arenaceous-argiUyte, 

 Calcareous-argillyte, Dolomitic-argillyte, Ojihiolitic-arg illyte, Pyritic- 

 arg illyte, and Chiastolitic-crrg illyte. Structural varieties are coarse, 

 fine, crumpled, spheroidal, concretionary, nodular, conylomeritic, knotty, 

 full of small nodules or concretions, giving the rock a knotty aspect, 

 irreyular, ohlique, and rihaned, the latter variety heing rather common.* 



Micasyte. — This rock is par excellence the typical schistose rock of 

 the country, its varieties in composition heing nearly innumerahle, and 

 some one or other of these varieties graduate into one or other of 

 every kind of schist. In composition the piincipal varieties are 

 argillous-micasyte, tico-micasyte, quartzitic-micasyte, liornMendic-micasyte, 

 cMoritic-micasyte, talcose-micasyte, garnet if erous-m icasyte, felsitic- 

 micasyte, calcitic-rnicasyte, dolomitic-micasyte, opluolitic-rnicasyte, and 

 2)yritic-micasyte. Any of these varieties may graduate in one of the 

 schists hereafter enumerated ; moreover, two or more of these vaiieties 

 may he comhined, fonning endless suh-varieties. 



]\Iicasyte has similar stractiu-al varieties to argillyte, and in addi- 

 tion to these the peculiar fi'illed structure previously deserihed is 

 common ; also, it may he gneissoid, through vrhich it graduates into 

 gneiss. Two suhvarieties of quartzitic-micasyte deseiwe special 

 mention and description. One is filrous-rnicasyte, in which the quartz 

 is aiTanged in thin stalks or layers, giving the rock a woody aspect. 

 In some the stalks are long and iri-egulai-, while in others they are more 

 or less ovate. "When the inliers of quartz are oval, a cross section of the 

 rock has a marked character fonning a more or less regiilar net-work. 

 In the second there are small, thin, round, slightly elongated discoid 

 pieces of quartz scattered thi'ough the rock, sometimes sparingly hut 

 often thickly together. The rock when weathered has the appearance 

 of heing scattered over or stuck full of small pieces of money fi'om the 

 size of a silver penny to that of a sixpence, from which the rock might 

 he called nummoid or money-schist. The fibrous and nummoid-schists 

 gxaduate into one another. 



Quartzyte or Quartz-schist. — Quartz-schist to me seems to be 

 given a prominence to which it is not entitled, as quartz-schist among 



* Other varieties may occur, but in this and all other lists only the rocks 

 obsei'ved are mentioned. Pai-ticular descriptions of the varieties are unnecessary, 

 as they ^vill be foimd in the different ■^orks on Peti-ology ; therefore, in this essay, 

 the only varieties that ■vrill be minutely described are those that are peculiar. 



