438 MISS E. M. K. WOOD ON THE LOWER LUDLOW [May I9OO, 



small gully (14 in fig. 6, p. 435) north-east of the main road-section. 

 Still farther; north-east, in an old quarry south-east of Tremaen 

 Farm (15), dark flaggy mudstones, weathering into minute fragments, 

 yield abundant fossils : — brachiopods, trilobites, cephalopods, etc. 

 It is difficult to say what is the exact horizon of these beds ; they 

 may possibly represent the Wenlock Limestone. 



In a quarry near Llanfaredd Church, 1 mile south of Rhiw 

 Rhwstyn, hard calcareous flags occur, with limestone-bands and 

 nodules crowded with Pentamerus and other brachiopods. This no 

 doubt represents the Wenlock Limestone, and thus marks the base 

 of the Lower Ludlow Beds. 



(c) Section in the Kiver Edw, Aberedw. — I have not 

 examined the various exposures seen along the hillside south of 

 Llanfaredd, but at Aberedw itself I have found the typical Mono- 

 graptus leintwardinensis in considerable abundance. It occurs, 

 associated with small specimens of Lingula lata, in the craggy cliffs 

 of the River Edw. Owing to the steepness of the banks, the beds 

 have slipped down from above in large masses, and it is often 

 difficult to say with certainty whether the beds are in situ or not. 

 The beds here too are much folded, and the strike changes every 

 few yards. The graptolites occur at one or two horizons among 

 a considerable thickness of dark micaceous and calcareous unfossil- 

 iferous flags. Unfortunately I have been unable here to determine 

 the relations of this zone to the graptolite-zones below, for the beds 

 appear to be, on the whole, barren of fossils. 



(d) Summary . — The succession , then, of the Lower Ludlow Beds 

 in the area east of the Wye is, in descending order, as follows : — 



(4) Hard calcareous flags and mudstones with bands rich in brachiopods : 



Pentamerus Knightii, Dayia navicula, etc. Zone of Monograptus 



leintwardinensis. 400 feet? 

 (3) Light-coloured shales passing up into flaggy mudstones. Zone of 



Monograptus scanicus. 250 feet. 

 (2) Shales and thin limestone-bands. Zone of Monograptus ~\ 



Nilssoni probably. The upper beds are more I AC\c\\ n &^c\e <-? 



micaceous and flaggy, and less fossiliferous. 

 (1) Dark calcareous flags. Zone of Monograptus vulgaris.) 



The upper limit of the Lower Ludlow Beds has not been 

 determined in this area. 



(5) Comparison of the two Areas. 



In the eastern part of the Builth district, therefore, one richly 

 graptolitiferous zone occurs, that of M. scanicus, which would 

 seem to be unrepresented in the area lying south and south-west 

 of Builth, while' at the same time the zone of M. Nilssoni is less 

 richly fossiliferous. As regards the comparatively poor develop- 

 ment of the M.-Nilssoni zone, it may be possibly due to the lack 

 of exposures at the right horizon ; but at all events it is certainly 

 not so thick as it is in the Irfon and Yicarage-road sections. 

 There is no doubt, however, that the M.-scanicus zone is absent a* 



