[ 557 ] 



XXXIV. — Notes to accom'pany some Fossils collected hy the Author, and 

 Mr. H. Still, F.G.S., during their employment on the Ordnance Survey 

 in Pembrokeshire. 



By HENRY MACLAUCHLAN, Esq., F.G.S., 



Employed on the Ordnance Survey. 

 [Read June 16, 1841.] 



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 Pem- 

 broke ; 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 hase for our observations, commencing at Llawhaden, a little 

 north of Canaston Bridge (fig. 2. p. 559), where the dip is northerly, and proceed- 

 ing 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-fran. 



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 of the section. 



These shales bear so strong a resemblance to the coal-measures, that unsuccessful 

 excavations have been made in them at Rudbaxton, Clarbeston, and Clynderwen, 

 south-east of Llandysilio. 



Indications of an anticlinal line may be seen near Narberth and Camrose, also 



VOL. VI. SECOND SERIES. 4 C 



