Dr. KiDD on the Mineralogy of St. Davld'^. 85 



spersed with low rocky cliffs, which rise higher and higher in ad- 

 vancing to the southern extremity ; at which point the rocks are 

 particularly interesting from their variety ; passing, sometimes 

 abruptly, from the coarsest grained conglomerate, as from its appear- 

 ance it might be called, to the finest schist. 



The prevailing colours of these rocks are green and brownish 

 'purple ; those colours alternating occasionally as in striped jasper. 

 The cement of those parts which resemble a conglomerate appears 

 to be in a great measure of chemical origin ; containing minute 

 crystals of semitransparent felspar, with small particles of glassy 

 quartz. It seems worthy of remai'k, that in those parts of the rock 

 which resemble a conglomerate, the pebble-shaped nodules of quartz 

 are very frequently of the same purple colour as the schist. The 

 sand of this beach when viewed through a microscope is seen to be 

 a mixture of fragments of shells with small particles of variously 

 coloured quartz and slate. A portion of it weighing !200 grains, 

 which had been collected in July 1811, and had been kept in a 

 room without a fire till March 1812, only lost one grain of its 

 weight by exposure to a heat of 212°: after which, having been 

 boiled in diluted muriatic acid, and then filtered, washed, and dried 

 by the same heat, it weighed 157 grains ; having lost tVV or rather 

 more than i of its weight, which may be considered as very nearly 

 the proportion of calcareous carbonate contained in this sand. The 

 sand is extensively used as a manure. 



Porthclais. 



This is a small fishing harbour situated to the south or south east 

 of St. David's, and is the termination of a narrow shallow valley, 

 Tvhich extends two or three miles inland, and is longitudinally 



