436 MISS E. M. R. WOOD ON THE LOWER LUDLOW [May 1 9OO, 



which were practically ungraptolitiferous in the district lying 

 south of the Wye, here contain abundant graptolites. 



(a) Section from Cnithio Brook to Rhiw Rhwstyn. — In 

 the brook at Cnithio Sawmill undoubted Wenlock Shales occur, 

 belonging to the zone of Cyrtograptus Lundgreni. From the brook 

 the ground rises somewhat rapidly, the beds becoming increasingly 

 flaggy, but no good exposures are seen for some distance up the 

 hill. In an old quarry (1 in fig. 6, p. 435), however, below 

 Pen-Cloddiau Farm, hard bluish-grey flags occur which contain 

 abundant graptolites, species of Orthoceras, and brachiopods. The 

 graptolites belong to the species Monograptus vulgaris and M . dubius, 

 but they are badly preserved and much distorted, owing to the 

 cleavage that the rocks have undergone. I class these beds un- 

 hesitatingly with the Lower Ludlow, but the exact position of the 

 base of this formation cannot be determined with certainty. 



The next exposure is some distance farther up the hill, in a small 

 quarry on the right of the road (2). Here occur two narrow 

 limestone-bands, about 5 or 6 inches thick, separated by 18 inches of 

 shale. The lowest limestone-band has yielded no fossils, but the 

 upper one, which is yellowish-brown and thoroughly rotten, is 

 crowded with M. colonics and Orthoceras, similar to the rotten 

 limestones seen in the Vicarage road-section. It probably, therefore, 

 represents the zone of M. Nilssoni, but this is the only locality 

 where I have detected it, and I have not hitherto found either 

 M. Nilssoni or M. boJiemicus in this eastern area. 



As we ascend the section the shales become more micaceous and 

 graptolites are rare, and I have only identified M. clubius with 

 certainty. The beds dip 10° east of south at an angle of about 

 16°. At (3), where the road bends sharply and the slope of the 

 hill increases rapidly, graptolites occur in abundance, and a complete 

 section is seen up to the top of the hill. For the first 75 yards the 

 beds consist of greyish-brown shales which have yielded M. scanicus 

 (common), M. chimcera (common), M. dubius, etc. As the beds 

 become increasingly flaggy, M. Rosmeri and M. bohemicus appear 

 together with 31. scanicus and M. chimcera. At (5), about 150 yards 

 from the bottom, light-brown, micaceous, flaggy mudstones have 

 almost entirely replaced the shales, and a thin calcareous band, 

 composed largely of the casts of Dayia navicula, intervenes. It was 

 apparently at this horizon that the officers of the Geological Survey 

 drew the boundary between the Wenlock and Ludlow formations. 

 Immediately above it come a few feet of a shale which has yielded 

 several specimens of 31. bohemicus. The occurrence of this graptolite 

 so high up in the Lower Ludlow is of interest, as it bears out the 

 evidence obtained in the Ludlow district of the long range of 

 the species. The shale is followed by a considerable thickness of 

 flaggy mudstones (6) which, however, have yielded no graptolites. 



(b) Confirmatory Aberedw Hill-Sections. — A section 

 confirmatory of the foregoing is seen in the small stream-course 

 immediately south of Ehiw Rhwstyn. Here only the uppermost 



