Extract

It may be proper to state, that it is owing to the encouragement held out by Colonel Colby to notice objects connected with science, where so doing does not interfere with the progress of the survey, that these fossils were collected.

In. Mr. Murchison’s work on the Silurian System the rocks of South Pembroke are described, and some general observations are made on those of North Pembroke; and in his map the lower beds of the Llandeilo Flags range from Camrose on the west to Llandewy Velfry on the east.

Taking this line as a base for our observations, commencing at Llawhaden, a little north of Canaston Bridge (fig. 2. p. 559), where the dip is northerly, and proceeding towards Precelly Mountain, we cross a conglomerate, which may be traced in a westerly direction to Ford, where it is found in contact with the trap; and in an easterly direction towards Llangan, where a stratified, conglomerate sandstone occurs, containing species of Trilobites and of Orthis or Spirifer.

To this conglomerate succeed first sandstone and sandstone shales, dipping to the north; and then, nearer Clarbeston, carbonaceous shales, containing casts of fossil shells and Graptolites, overlaid by limestone. The line of section afterwards crosses another bed of sandstone, which is succeeded by roofing-slates that extend nearly to Llys-y-frân.

Similar carbonaceous shales may also be seen to the west of the line of section at St. Catherine’s Bridge, near Camrose, and at Rudbaxton; also at Long Ford, south of Llandysilio, to the east