434 MISS E. M. R. WOOD ON THE LOWER LUDLOW [May I900 y 



The following is the succession in descending order : — 



(5) Light-brown flaggy shales with Monograptus bohemicus, M. Nilssoni, 



M. colonus, and Retiolites spinosus (rare). 4| feet. 

 (4) Thin reddish-brown limestone, containing M. colonus in abundance and 



numerous fragments of shells, etc. 3 to 4 inches. 

 (3) Shales (same as 5) with M. bohemicus, M. Nilssoni, M. colonus, and 



Eetiolites spinosus (abundant). 8| feet. 

 (2) Thin limestone, made up of fragments of trilobites, brachiopods, 



crinoid- stems, etc., and containing M. colonus. \ inch. 

 (1) Alternating dark flaggy and fissilej shales containing M. INilssoni,. 



M. colonus, and Eetiolites spinosus in bands. 12 feet. 



This section is prolonged without much interruption for 40 or 

 50 yards ; the paler shales predominate, some beds being of the 

 nature of mudstones, others more shaly. The same graptolites 

 occur, but are for the most part fragmentary and rare. There 

 are no more exposures for 150 yards; then at c 2 occur thin, light- 

 brown, papery shales with limestone-nodules, and flaggier beds 

 containing a few badly-preserved graptolites, M. colonus (?), and 

 various mollusca. At c 3 the ground rises steeply, owing to the 

 increasingly flaggy nature of the beds and the decrease of argillaceous 

 material, while the graptolites (31. colonus, Retiolites ?) are relatively 

 few, and finally seem to disappear altogether. At d the beds 

 are flaggy, yellowish-brown mudstones, breaking with conchoidal 

 fracture : they have yielded no graptolites, and only a few small 

 brachiopods. 



The rich graptolite-bearing shales (c 5 ) with the underlying flags 

 (b 2 ) are exposed east of Gloew Brook, near the Oaklands, but I have 

 not traced them farther eastward. 



The thin papery shales seen at cr and c 3 at the base of the arena- 

 ceous series are also exposed in the Maesmynis road, beyond the 

 Smithy, and in the Nant-yr-Arian (c 6 ), but graptolites are for the 

 most part rare and indifferently preserved, and I have identified only 

 M. dubius and M. colonus. The succeeding mudstones and flags 

 are seen in various quarries and exposures farther south (see maps, 

 figs. 4 & 5, pp. 430 & 432) ; but search for graptolites in any of 

 these higher Ludlow Beds in the district south of Builth has so 

 far proved practically fruitless, and therefore it would seem impossible 

 in the meanwhile to fix the upper limit of this formation by means 

 of graptolites. Everywhere the beds are mudstones and calcareous 

 flags, rich in brachiopods, with here and there traces of graptolites 

 showing that they had not altogether died out ; thus, in a small 

 quarry along the roadside, about ^ mile south of Maesmynis, I 

 found a few fragments which probably may be referred to M. leint- 

 wardinensis. Still farther south, along the banks of the Duhonw, 

 the rocks are dark micaceous flags with splintery fracture; these higher 

 beds, however, though apparently well adapted for the preservation 

 of graptolites, have, so far, yielded none. Judging from the evidence 

 obtained at Aberedw, which lies to the south-east, I believe that 

 these flags belong to the M.-leintwardinensis zone ; and as that 

 species occurs only in certain bands among a great thickness of 

 unfossiliferous beds, it is possible that it may yet be found here. 



