~ BENT AND WAVED SLATE. 37 
first instance and principally, to atmospheric in- 
fluences ; for, in some places, as at the slate quarries, 
this presumed decomposition shews itself throughout 
the whole depth to which the rock has been work- 
ed—at one spot, the rubbly and loose state of the 
rock gradually disappearing, and the substance by 
degrees getting closer, until it is fairly of the cha- 
racter of “ dunstone,” or at the least of ordinary 
slate, Indeed, this transition from loose to indurated 
slateis exemplified mostfreely in thisneighbourhood, 
and seems to be inconsistent with a supposition of 
decay from the agency of air. The oxide of iron 
occasionally stains our slate in fantastic shapes. It 
seems also, to occur in greatest plenty in the imme- 
diate neighbourhood of fossils, and in their compo- 
sition. 1 occasionally find fragments of slate in the 
quarries on which are marked, dark, broad, concen- 
tric lines, in the manner of the layers of wood in 
the boles of trees, of which appearances I can offer 
no explanation. 
There is one fact in the history of our slate 
worthy of notice, and worthy of being further inves- 
tigated with a view to some explanation. ‘This is 
the bendings or reflections in the slope of the rock, 
observed in very many places. In one spot in par- 
ticular, I have observed it to be bent four times 
in the depth of as many feet, so as to assume a per- 
fectly zig-zag appearance. It must be recollected, 
that this occurrence is not limited to loose and 
disconnected kinds of slate, but may be seen on 
larger scales in good solid sorts also, though the re- 
peated reflexions may not be here so remarkable or 
perfect.* At Crabtree, near Plymouth, there is a 
* Ata spotcalled Meadow-foot, at the mouth of the Erme how- 
ever, this convoluted and zig-zag condition of slate is assumed in 
good solid rock on a very extensive scale, the whole shore being 
composed of arenaceous schist, putting on the same undulated 
