376 MISS G. L. ELLES ON THE WEDLOCK [May I9OO, 



this horizon, though it has not yet become a common form. The 

 zone is also exposed for some little distance along the strike of the 

 beds behind Grove Cottages, on the Rhayader road ; the beds are 

 striking N. 40° E. 5 and yield the forms recorded in Table I, col. E 

 (p. 378). 



The only other exposure of the M.-riccartonensis zone is to be 

 found on the banks of the Wye. This section is interesting, because 

 it affords a means of detecting the alteration in the strike of the 

 beds as they sweep round the exposure of Llandeilo rocks. At 

 first the beds strike N. 30° E., then they bend gradually away, till 

 a little way below the railway-bridge the strike is N. 60° E., and a 

 short distance above the bridge the beds run very nearly due 

 north and south. Here the beds are very poor in fossils. Mono- 

 graptus capillaceus, Tullb., and M. dubius were the only graptolites 

 found. M. capillaceus seems to be entirely confined to this zone 

 of M. riccartonensis : it often occurs in abundance, associated with 

 the zone-graptolite, and it may be taken to indicate the zone even 

 where the typical fossil itself is not very common. 



It is unfortunate that the best exposure of the M.-riccartonensis 

 zone is a little outside the area with which I am dealing. It occurs 

 on the other side of the fold, where exposures are by no means 

 numerous, and is to be found on the banks of the Ithon, where 

 that stream makes a big bend north-east of Newbridge ; at this 

 locality M. riccartonensis and M. capillaceus are very abundant. 

 The M.-riccartonensis zone probably attains a maximum thickness 

 of about 300 feet. 



(3) Zone of Cyrtoyraptus symmetricus, sp. nov. — In the 

 south-western parts of the district a considerable thickness of 

 flagstones succeeds the M.-riccartonensis zone. These beds are 

 exposed above the railway-bridge on the Wye, in the railway- 

 cutting near Builth Road Station and south-east of the Wye, in 

 a small quarry east of the station, and in the road leading to it. 

 These beds, however, which are of the nature of coarse sandy flags, 

 seem to die out north-eastward. They are certainly not present 

 at Castle Crab, where the highest beds of the M.-riccartonensis zone 

 are followed in an apparently normal succession by beds in which 

 C. symmetricus is the characteristic form. 



The beds belonging to this zone consist of alternations of hard 

 flagstones with very soft fissile shales, which have a tendency to 

 weather deeply. The zone is best exposed in a small quarry, in a 

 field south-east of Castle Crab, which has been excavated across 

 the strike. The strike here runs N. 30° E., and the beds dip at 

 30°, N. 30° W. They consist almost entirely of the softer shales, 

 and are very fossiliferous ; they have yielded the graptolites enume- 

 rated in Table I, col. F 2 (p. 378). Orbiculoidea, Chonetes minima, 

 Cat diola interrupted and Orthoceras sp. are also found. 



Beds with a similar fauna were discovered up an old cart-track, 

 which leaves the road just where it bends towards Castle Crab, behind 

 €astle Crab, at the top of the quarry mentioned above, and in 



