ili GEOLOGY OF ARRAN. 



nautilus, being the only animals of this order yet found in 

 the lower Permian beds. 



Still advancing eastwards, we meet with several other dikes. 

 One of these is depressed ten feet in the tideway, is on a level 

 with the sandstone along the grassy surface at the base of the 

 cliffs, and in the front of the cliff is again worn, forming a 

 deep chasm, which is bounded eastwards by a bold projecting 

 edge of the cliff, crowned with wood. The dike on the beach, 

 and fissure aloft, are about fourteen feet wide each, but not 

 exactly in the same direction, the dike sustaining here a con- 

 siderable undulation. 



36. We now reach the great bed of claystone, the largest 

 upon this coast, and presenting many interesting appearances. 

 It forms a vein rather than a bed, as it is placed at an angle 

 of about 15 with the sandstone strata. The sandstone dips 

 S. 12 E. at about 15, while the claystone vein is inclined 

 in the same direction at an angle of about 30. The rock is 

 divided irregularly into prisms by joints perpendicular to the 

 lower surface of the vein, so that the prisms lean back towards 

 the south, giving the appearance, when viewed casually, of a 

 bedding directed northwards. The structure at the upper 

 surface is often schistose at right angles to the joints, or in the 

 direction of the vein. The base is of a uniform texture, of 

 felspathic substance, with quartz pieces imbedded. The 

 structure varies from a uniform claystone, or clinkstone, to a 

 small-grained porphyry. The colour is pale yellow, or yellow- 

 ish-white ; and at the first view the rock might be taken for 

 a sandstone : it has indeed been described, when seen in its 

 continuation in the adjoining cliff, as a white columnar sand- 

 stone (Headrick's Arran, p. 66). The rock on which it rests 

 is a conglomerate; that beneath which it plunges southwards 

 is fine-grained sandstone. The upper surface of the vein is 

 very rough and jagged, with no resemblance to the style of 

 decomposition among sandstones. The breadth exposed upon 

 the shore is between thirty and forty yards. Along the level 

 shore, where the vein rises to the north, its lower surface is 



