TRAP AND ALTERED ROCKS, CAERMARTHENSH1RE. 



363 



Organic Remains in the Cambrian Rocks of Caermarthenshire. 



Besides the crinoidea, and a few traces of shells detected in the beds of passage be- 

 tween the Llandeilo flags and the Cambrian rocks, singular forms have been recently 

 discovered near Llampeter, in the faces of the building- stone of that place. 



This discovery was made by the Rev. A. Ollivant, Professor of Llampeter College, 

 and the specimens procured by him are delineated. (See PL 30.) These convoluted 

 forms seemed at first sight to represent zoophytes, but after a long examination, no 

 zoologist has ventured to pronounce that they ever belonged to the animal kingdom. 

 Neither has the botanist been willing to recognise them as vegetables, although in com- 

 mon with the zoologist, he allows that they have a regularity of form which indicates 

 organic structure. 



Trap and Altered Rocks in Caermarthenshire. 



When I commenced the examination of South Wales, I was, like other geologists, 

 unacquainted with any trap rocks in Caermarthenshire ; nor did I discover any trace of 

 them till the summer of 1833. The spot at which they were first seen is in the rocky 

 knoll of Blaen-dyfFrin-garn, on the left bank of the Sowdde, about three miles south-east 

 of Llangadock, and about one and a half mile north-west of Pont-ar-lleche, where the 

 Old Red Sandstone and the Silurian rocks are conterminous. Seeing the great extent 

 to which all the formations of this neighbourhood had been dislocated, I was anxious to 

 discover any rock of intrusive character which might explain such operations, yet this 

 knoll was for some time the only one I could detect. 



This trap is more or less porphyritic, having a base of compact felspar partly concretionary, and 

 sometimes beautifully mottled by green earth. It occasionally contains a little lime. The structure 

 is both amorphous and flaglike. These varieties protrude at various points along the summit and 

 upper sides of the hill. A black flagstone and shale, which dip from its south-eastern face, are not 

 seen in contact with the trap, but at the distance of more than one hundred paces, and near the 

 base they are thrown off at an angle of 30° to the south-east, and in a state of hard, black, slightly 

 calcareous flag, which has been quarried, and in which was found the beautiful small trilobite called 

 Trinucleus Lloydii, (PL 23. f. 4.) On its western, north-western, and south-western faces, this 

 little ridge tilts off sandstone, which has been shown to form a part of the Caradoc formation. It 

 is most instructive to observe how precisely similar is the effect of this contact, to that described 

 in the Wrekin, the Caradoc, &c, where trap has thrown up sandstone of the same age. Near the 

 north-western face of the knoll, the sandstone resting on the trap is a complete quartz rock of con- 

 choidal fracture, the grains of sand exhibiting all the appearance of having been agglutinated into a 

 hard, homogeneous mass. On the side above the farm-house of Prenteg, this altered rock presents 

 - a bold and rugged vertical face, of about sixty feet in height, in which there are slight traces of 

 bedding, the whole resembling a confused assemblage of huge trapezoidal blocks, above which the 

 quartz rock assumes a stratified structure, and about thirty paces distant from the nearest boss of 



