CURVED STRATIFICATION. 
section will show that each of the formations 2,3,4 are re^ 
peated thrice at the surface, twice with a southerly, and once 
with a northerly inclination or and the beds in No. 1, 
which are nearly horizontal, are still brought up twice by a 
slight curvature to the surface, once on each side of A. Be¬ 
ginning at the north-west extremity, the tile-stones and con¬ 
glomerates. No. 4 and No. 3, are vertical, and they generally 
form a ridge parallel to the southern skirts of the Grampi¬ 
ans. The superior strata. Nos. 2 and 1, become less and less 
inclined on descending to the valley of Strathmore, where 
the strata, having a concave bend, are said by geologists to 
lie in a ‘‘ trough ” or “ basin.” Through the centre of this 
valley runs an imaginary line A, called technically a “syn¬ 
clinal line,” where the beds, which are tilted in opposite di¬ 
rections, may be supposed to meet. It is most important for 
the observer to mark such lines, for he will perceive by the 
diagram that, in travelling from the north to the centre of 
the basin,he is always passing from older to newer beds; 
whereas, after crossing the line A, and pursuing his course in 
the same southerly direction, he is continually leaving the 
newer, and advancing upon older strata. All the deposits 
which he had before examined begin then to recur in re¬ 
versed order, until he arrives at the central axis of the Sid- 
law hills, where the strata are seen to form an arch, or sad¬ 
dle^ having an anticlinal line, B, in the centre. On passing 
this line, and continuing towards the S.E., the formations 4, 
3, and 2, are again repeated, in the same relative order of 
superposition, but with a southerly dip. At Whiteness (see 
diagram) it will be seen that the inclined strata are covered 
by a newer deposit, a, in horizontal beds. These are com¬ 
posed of red conglomerate and sand, and are newer than any 
of the groups, 1, 2, 3,4, before described, and rest unconform- 
ably upon strata of the sandstone group. No. 2. 
An example of curved strata, in which the bends or con¬ 
volutions of the rock are sharper and far more numerous 
within an equal space, has been well described by Sir James 
Hall.* It occurs near St. Abb’s Head, on the east coast of 
Scotland, where the rocks consist principally of a bluish 
slate, having frequently a ripple-marked surface. The un¬ 
dulations of the beds reach from the top to the bottom of 
cliffs from 200 to 300 feet in height, and there are sixteen 
distinct bendings in the course of about six miles, the curva¬ 
tures being alternately concave and convex upward. 
Folding by Lateral Movement.—An experiment was made 
by Sir James Hall, with a view of illustrating the manner in 
* Edin. Trans., vol. vii., pi. 3. 
