South-Western Part of Somersetshire* 367 



the east of Minehead to that at the mouth of the river Parret there 

 is a rocky shore, bounded by precipitous cHffs, rising in many, 

 places to the height of 100 feet. These are chiefly formed of that 

 variety of secondary limestone, so well known by the name of 

 lyas, together with the red argillaceous rock described § 30. The 

 boundaries of these rocks will appear by inspecting the map, and I 

 shall now point out the more remarkable circumstances connected 

 with each. The great disturbances which have taken place in the 

 strata render it extremely difficult to ascertain with precision the re- 

 lative positions of these two rocks. When I first examined the 

 coast, I observed what I conceived to'be the most distinct evidence of 

 the red rock alternating with the lyas : but as this was an important 

 point to ascertain, being at variance with all observations in other 

 places of the position of the lyas and red rock which 1 had heard of, I 

 repeated my examination of the ground with great care, and I think 

 it is probable that the apparently very distinct alternations of the 

 lyas strata with the red rock are deceptions produced by those 

 curvatures and dislocations so common on this coast, as I shall 

 shew when I describe those places. This lyas is an argillaceous 

 limestone of a dull earthy aspect, with a large conchoidal fracture, 

 and generally of a light slate blue colour. It occurs in very regular 

 strata which seldom exceed a foot in thickness, and are often not 

 more than four inches : they are separated from each other by strata 

 of slate clay, varying considerably in thickness. All the strata of this 

 limestone, though externally very similar, are not of the same mine- 

 ralogical composition, for they have very distinct properties. Some 

 of them yield a lime which possesses in a most eminent degree the pro- 

 perty of setting under water : these are generally the thinest strata, 

 are of a light blue colour and compact earthy texture ; on each sur- 

 face of the stratum, and at the joints the colour is changed to a light 



