12 DESCRI PTION of the 



thinly lamellated, of a filky luftre, and faponaceous to the feel : 

 it clings round thofe mafles in all their variety of direction, and 

 of courfe its texture is there much twifted. When the argillite 

 ftratification has extended its thicknefs to near three quarters of 

 a mile, the limeftone which I have mentioned above then occurs, 

 in a bed of twelve feet thick. Its colour is bluifh- black; and it 

 is much pervaded by veins of quartz, and of calcareous fpar ; 

 the lad of thofe are, in many places, of considerable breadth, and 

 are of a pale flefh colour. Where this limeftone has been 

 wrought, I obferved it forked ; that is to fay, the bed is there 

 fplit or divided into two, by the intervention of an argillaceous 

 body. Upon each fide of this bed of limeftone the argillite oc- 

 curs of two colours. That which is next to, and in contact with 

 the limeftone, is black, of a fhaly texture, foils the hand, and has 

 veins of ferruginous-coloured quartz trending through it. The 

 argillite which is more remote from the limeftone is of a dark 

 purple colour. 



Immediately after this narrow bed of fhale, the argillite re- 

 aflumes its greenifh-blue colour, and flaty texture, and becomes 

 highly indurated : here fome fpecks of granulated quartz begin 

 to appear, thinly fcattered in its mafs, and, foon after, it is feen 

 to pafs over into an aggregate rock, chiefly compofed of grains 

 of quartz, felfpar, and minute particles of mica. The particles 

 of quartz and of felfpar feldom occur in this aggregate larger 

 than the eight of an inch : thefe have very little the appearance 

 of having fuffered attrition : they are much mixed, and are fre- 

 quently feen to take lineal directions ; and in thofe lines the par- 

 ticles of felfpar have frequently a comprefTed appearance, and an 

 eye-like form. This rock, in mafs, has a grey ifh- blue colour: 

 it is of great induration, and although lamellous or flaty in its 

 texture, a crofs fracture is often more eahly obtained than one 

 with the lamella?. Its crofs fracture is pretty even, but appears 

 more granular than foliaceous. This rock occurs frequently in 



the 



