CLEAVAGE OF THE ROCKS OF THE NORTH OF SCOTLAND. 
461 
thicker line represents the central axis of an arch of foliation. The dotted lines 
show the direction supposed to be followed, in unexamined districts, by the lines just 
explained. All the lines are laid down on the Map with more continuity and regu- 
larity than really exist ; this error can only be fully corrected by a minute examina- 
tion of the whole country. 
As the object of the sections (figs. 3, 4 and 5) is to show the direction of the dip of 
the foliation and cleavage, continuous lines have been used to represent them, while 
the dotted lines mark the stratification. 'J^he contortions of the foliation are indicated 
conventionally, as is explained at p. 447, since it would not be possible to represent their 
real complication on so small a scale. In fig. 2 the upper line is an ideal completion 
of the curves indicated by the dips of the foliation and cleavage seen in fig. 1, and 
the lower line is a rough sketch of the outline of the country ; but it is not intended 
to be inferred that the rocks ever reached up to the upper line. In all the sections 
the scale of height considerably exceeds that of length, but the angles of dip are pre- 
served as nearly as the observations taken on a large scale over broad tracts of 
country admit of. 
Note . — The strike or direction of the foliation, cleavage and bedding on the plane 
of the earth’s surface was taken with a pocket-compass ; the corrections for the 
variation of the needle being derived from the directions on the Admiralty Charts ; 
viz. for the 
Forth 25’30 
Aberdeen 26‘30 
Banff 27 
Loch Ryan 27'30 
Loch Eil 28*20 
Isle of Lewis 30*94 
The angles of dip were taken with a pocket-clinometer, w'hich is sufl[iciently accu- 
rate for the object required, as the irregularity of the surfaces to be measured leaves 
all such observations liable to errors of 2° or 3°. 
