12 DESCRIPTION of the 
thinly lamellated, of a filky, luftre, and faponaceous to the feel : 
it clings round thofe maffes in all their variety of direction, and 
of courfe its texture is there much twifted- When the argillite 
{tratification 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 laft of thofe are, in many places, of confiderable 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 ar gillite re- 
affumes 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 
ef 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 comprefled appearance, and an 
eye-like form. This rock; in mafs, has a greyifh-blue colour: 
it is of great induration, and although lamellous or flaty in its 
texture, a crofs fracture is often more eafily obtained than one 
with the lamella. Its crofs fracture is pretty even, but appears 
more granular than foliaceous. This rock occurs frequently in 
the 
