Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/375

 the east of Minehead to that at the mouth of the river Parret there is a rocky shore, bounded by precipitous cliffs, 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 relative 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 mineralogical composition, for they have very distinct properties. Some of them yield a lime which possesses in a most eminent degree the property of setting under water: these are generally the thinest strata, are of a light blue colour and compact earthy texture; on each surface of the stratum, and at the joints the colour is changed to a light