PART I. CHAPTER V. 



65 



Curved Strata. 



horizontal, each oval pebble having originally settled at the bot- 

 tom of the water, with its longer side parallel to the horizon, for 

 the same reason that an egg will not stand on either end if 

 unsupported. Some few, indeed, of the rounded stones in a con- 

 glomerate may afford exceptions 

 to the above rule, for the same 

 reason that we see on a shingle 

 beach an occasional oval or flat- 

 sided pebble resting on its end 

 or edge. For some pebbles hav- 

 ing been forced along the bottom 

 and against each other, may 

 have settled in this position. 



Vertical strata, when they can 

 be traced continuously upwards 

 or downwards for some depth, 

 are almost invariably seen to be 

 parts of great curves, which may 

 have a diameter of a few yards, 

 or of several miles. I shall first 

 describe two curves of consider- 

 1 1> able regularity, which occur in 

 .2 1 Forfarshire, extending over a 

 - country twenty miles in breadth, 

 from the foot of the Grampians 

 to the sea near Arbroath. 



The mass of strata here shown 

 may be nearly 2000 feet in 

 thickness, consisting of red and 

 white sandstone, and various co- 

 loured shales, the beds being dis- 

 tinguishable into four principal 

 groups, namely, No. 1. red marl 

 or shale ; No. 2. red sandstone, 

 used for building; No. 3. con- 

 glomerate; and No. 4., grey 

 paving-stone, and tile-stone, with 

 green and reddish shale, con- 

 taining peculiar organic re- 

 mains. A glance at the section 

 will show that each of the for- 

 mations 2, 3, 4, are repeated 

 thrice at the surface, twice with 

 a southerly and once with a 

 northerly inclination or dip, and the beds in No. 1., which arc 



