186 
Mr. Weaver on the 
Loaves, and Bray Head ; but it contains very rarely rounded and 
angular grains of felspar, and a few scattered minute scales of mica. 
The pure Clay slate is yellowish, greenish, or purplish in 
colour, smooth, glossy, fissile, and free from admixture. 
1 hese two rocks arc interstratified not only on the large but on 
the small scale ; and it is in these alternations that reciprocal in- 
corporation takes place ; presenting rocks in some instances of an 
homogeneous uniform character, and in others of a distinctly com- 
pounded structure. In the former modification, quartz rock be- 
comes tinged throughout its mass of a yellowish, greenish, or pur- 
plish colour, by an infusion of the matter of clay slate, and passes 
occasionally even into hornstone and flinty slate. As the propor- 
tion of clay slate increases, the compound becomes entitled to the 
name of quartzy clay slate ; and at last it passes into pure clay slate, 
both compact and fissile. 
The beds in which quartz predominates are of a firm compact 
character, and scales of mica sometimes occur, disposed without 
order through their mass : in the slaty beds they appear frequently 
arranged in the direction of the lamina?, silvering over the plane of 
separation. 
Quartz rock impregnated with the matter of clay slate frequently 
envelopes grains of quartz, scales of mica, sometimes also grains of 
felspar, of a yellowish white or flesh red colour, and rarely, minute 
portions of clay slate ; thus constituting a firm compact variety of 
greywacke ; as at the northern foot of Great Sugar Loaf, in the 
Dargle, and in the south-eastern side of Bray Head. When clay 
slate matter predominates, it passes into greywacke slate. 
All these rocks are more or less traversed by small contempora- 
neous veins and strings of pure white quartz, which in their range 
frequently follow the line of the dip. Quartz rock in particular is 
