Yol. 52.] GEOLOGY OF THE NEIGHBOURHOOD OF CARMARTHEN. 523 



31. On the Geology of the Neighbourhood of Carmarthen. By 

 Miss Margaret C. Crosfield and Miss Ethel G. Skeat. 

 (Communicated by J. E. Marr, Esq., M.A., F.K.S., Sec.G.S. 

 Eead April 15th, 1896.) 



[Plates XXV. & XXVI.] 



Contents. 



Page 



I. Introduction and Bibliography 523 



II. Physical Structure 524 



III. The Succession and Detailed Description of the 



Beds 525 



IV. Comparison with the Deposits of other Areas ... 531 

 V. Description of some new Species of Trilobites ... 535 



VI. Conclusion 539 



I. Introduction and Bibliography. 



The area described in this communication has Carmarthen for its 

 centre, and lies approximately within a 4-mile radius of that town, as 

 indicated in the accompanying sketch-map (PI. XXV.). Our object 

 in examining this district was to trace the continuation of the com- 

 plex anticline which was discovered by the late Mr. T. Roberts, 

 about 10 miles west of Carmarthen. In the map illustrating his 

 .paper 1 the anticline is shown to be narrowing rapidly in the 

 -neighbourhood of Mydrim, the Didymograptus-\>ediS seem to wrap 

 round the older Tetragraptus series, and apparently the anticline 

 :is dying out. 



An examination of the beds round Carmarthen has enabled us to 

 * establish this conclusion, and to show that in our own district we 

 have a new anticline, the northern limb of which continues in the 

 ^same direction as that of the anticline farther we*c, but with a core 

 •consisting of older rocks, which we correlate with the Tremadoc 

 Slates. The southern limb of the new anticline is buried under 

 'Old Red Sandstone (which here encroaches farther north than at 

 St. Clears), but in the northern limb we have a regularly ascending 

 series from Tremadoc Slates to Dicranograptus-shales. To the east 

 this regular succession of beds is disturbed by the presence of an 

 extensive series of alternating grits and sandstones, with some 

 shales, the last containing Bala fossils. The beds in question abut 

 on those of Arenig age, but whether their appearance in this locality 

 is due to faulting or to an unconformity we cannot at present deter- 

 mine, owing to the nature of the ground and the exceedingly complex 

 character of the foldings. The clue to the relations of these beds 

 would doubtless be discovered by an examination of the area lying 

 to the east. 



1 Koberts, T., ' Notes on the Geology of the District West of Caermarthen,' 

 $uart. Journ. Geol. Soc. vol. xlix. (1893) p. 166. 



