Dr. KiDD on the Mhieralogy of St* David's, 87 



Parts of this rock resemMe Fullers' earth ; but from the occasion- 

 ally green colour and the peculiar direction of the natural rifts, 

 giving it a tendency to separate into rhomboidal or into wedge- 

 shaped fragments, it possesses a characteristic mark which serves ta 

 connect it with the prevailing rock of the neighbourhood. 



Many parts of this rock easily crumble into the state of an 

 earthy gravel, and are commonly used as a substitute for common 

 gravel in and about St. David's. 



I shall readily be excused for mentioning here, that there is in 

 the Ashmole Museum a specimen from Jersey so very like in its 

 general character to the part of the St. David's rock now under 

 consideration, that even an experienced eye might be deceived as 

 to its separate identity : and it adds to the interest of the comparison 

 of the specimens in question, that they both occur amongst a suite 

 of rocks composed principally of hornblende and felspar, and are 

 both used for the same economical purpose. 



Fortification near St. David''s. 



To the south west of St. David's are the remains of an old 

 entrenchment, situated near the edge of the adjacent cliff; and from 

 the further extremity of the entrenchment the cliffs run out at right 

 angles to the general bearing of this part of the coast, forming a 

 tongue of land which projects into the sea. In this projecting point 

 a natural arch exists, which has been probably excavated by the 

 gradual washing away of part of the rock ; presenting an appearance 

 somewhat like that represented in the third of Dr. Mac Culloch's 

 plates, in the first volume of the Society's Transactions. 



Near the extremity of this tongue of land is a vein of clay 



