

Vol. 62.'] ROCKS OF WESTERX CAER1TAETHEXSHIRE. 599 



As a natural outcome of these great closing-up movements, rocks 

 that had been deposited over wide areas and under very different 

 conditions have been brought together within the comparatively- 

 narrow limits of the district under consideration. In other words, 

 points that are now within 3 or 4 miles of one another were, 

 previous to the movements, four or five times that distance apart. 

 Certain beds in the northern limb of the fold are lithologically 

 distinct from corresponding beds, that is, beds of the same age, in 

 the southern limb ; and, what is of greater significance, there is 

 considerable difference in the character of the faunas. For instance, 

 on the south the Didymograptus-Murchisoni Beds, if at all present, 

 are very poorly developed ; the Asaphus-tyrannus Beds are highly 

 calcareous, and in one instance thickly-bedded limestones ; and the 

 Bala-Caradoc rocks are well developed, and contain two or three 

 strong bands of limestone. While on the north the D.-Murchisoni 

 Beds are well-formed and persistent ; the Asaphus-tyrannus Beds 

 are thin and ashy, with hardly a trace of calcareous matter ; and the 

 Bala-Caradoc rocks are represented by some blue-black mudstones 

 which make but a poor show. On the north, there is also a calcareous 

 development in the Dicranograp>tus-$h.ales with a rich graptolite- 

 fauna — features which are entirely absent on the south. (See 

 figs. 1 & 2, p. 600.) 



(2) Faulting. — The majority of the faults, as might be expected, 

 are strike-faults, running east and west. Those on the north 

 usually hade northward at various angles, many of them being 

 thrusts. On the south there are but few thrusts, the majority of the 

 faults being normal. There are very few dip-faults, and where they 

 occur they are of small extent. 



The rocks forming the core of the anticline are much crushed. 

 Especially is that the case along a line traced from near Banc-y-felin 

 to Llangynin Church, and thence to Aberddeunant. Near that place, 

 the line of disturbance probably splits, forming faults which account 

 for the features of the country farther west ; that is, the bringing to 

 the surface of older and more gritty beds north of Whitland — these 

 latter having also suffered much from folding and faulting. 



There is another line of disturbance running from near Asgood, 

 past Blue Boar and Llaindelvn to a point south of Clog-y-fran. This 

 disturbance presumably accounts for the disappearance eastward of 

 the Woolston and Clog-y-fran ashes. 



The ground round Clog-y-fran and Forest has been much affected 

 by faulting. At the former place, strata of Didymograptus-bifidus 

 and Asaphus-tyrannus age, and two types of Bala-Caradoc rocks, can 

 be studied in the farmyard ; and at the latter Bala-Caradoc rocks 

 have been sandwiched between two slices of D.-bijidus Beds in one 

 locality, and between D.-bifidus beds and Lower Llandovery (?) 

 beds in another close by, while the D.-bifidus Beds themselves, 

 including the ashes, have been very much cut up. 



The Bala-Caradoc rocks west of Llanddowror have also suffered a 

 Q.J. G.S. No. 248. 2x 



