GREYWACKE SLATE. Al 
in schistus,” (Carrington’s Dartmoor, Preface) also 
at Boveysand, side of the Yealm, &c. just as, schistus 
. may be seen, placed similarly in lime, independently 
of any suspicions of these insulated patches having 
been thrust up in the manner supposed by Mr. Hen- 
nah, or occurring thus through Plutonic agencies. 
This kind of insulation of slate may be noticed on 
the hill leading from Stonehouse to Devonport. 
Striking alternations of these strata are also not 
uncommonly observed, as at Prince Rock and Kitley 
Hill, both near Plymouth, east bank of the Tamar 
(where greywacké, slate, and lime are found to alter- 
nate), and in several instances also, I have observed 
lime and slate at their point of junction, forming an 
intermediate kind of stone, a fact likewise noticed 
in the-case of the lime and slate of Westmoreland, 
where lime mostly rests on slate, and in approaching 
it, gradually gets slaty. Schistose lime occurs at 
St. Mary Tavy, close to Dartmoor.’ 
The greywacké slate of the coast, besides the 
ordinary lead colour, presents several others, some 
particularly pleasing to the eye—green (with minute 
fossils,) drab, purple, purplish drab, golden yellow 
in small patches, olive, and silvery drab. A deal 
of this schist is employed for coarse flooring in cot- 
tages, and some for mantel pieces. Its fracture 
being conchoidal, itis used with great facility in the 
formation of very strong and solid masonries.* 
Argillaceous schist not unfrequently exists in small 
beds, the fracture of which is prismatic, this may 
* The generality of slate forms a remarkably durable building 
stone. Its appearance is greatly against a belief of such a fact, 
and if laid horizontally it would probably endure but a very 
limited time; when laid vertically however, so as to allow water 
to run off, its durability is astonishing ;—a piece of the “ old wall 
of Plymouth,” now nearly two hundred years old, which I have 
seen, and is built of common grey slate, seems to have suffered 
little from the action of time. 
G 
