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ME. D. C. EVANS ON THE ORDOVICTAN [Nov. I906, 



(3) Conclusions.- — These beds seem to have been deposited 

 under conditions exceedingly suitable for the preservation of 

 6 forked ' graptolites. Many of the bedding-planes are covered 

 with a perfect mat of these fossils, while biserial and other types 

 of twin graptolites are comparatively rare. 



The lighter stripe is due to a thin layer of more ashy material, 

 and the ash-band is presumably a ' light ' stripe of larger dimensions, 

 owing to greater activity in. the production of the material. 



(d) Llandeilo Group : As aphus-tyr annus Beds. 



(1) South of the Anticline. — The beds occurring on the 

 south of the anticline are of the typical description, and consist of 

 black limestones and calcareous black shales. The fossils are of the 

 usual type, and include : — 



Asaplms tyrannus, Murch. 

 Ogygia Buchii, Brongn. 

 Homalonotus. 



Trimiclcus Lloydii, Murch. 

 TrinucUus fimbriatus, Murch. 

 Trinucleus favus, Salt. 

 Calymcne brevicapitata, Portl. 

 Calymenc cambrensis, Salt. 

 Acidaspis of. Jamesi, Salt. 

 Beyrichia complicate*, Salt. 

 Fa coxites sp. 

 Orthis striatula, Emm. 

 Ortkis vespertilio, Sow. 



Orthis calligramma, Dalm. 

 Orthis testadinaria, Dalm. 

 Orthis elegantula, Dalm. 

 Orthis biforata, Schloth. 

 Orthis triangularis, Sow. 

 Strophomena corrugatclla, Dav. 

 Sirophomena compressa var. llan- 



deiloensis, Salt. 

 Siphonotreta micula, M'Coy. 

 Lingula granulata, Phill. 

 Lingula cf. attenuata, Sow. 

 Leptcena cf. sericea ; etc. 



There are only three localities where these beds come to the 

 surface, and all of them lie on the line of an extensive east-and- 

 west fault, which accounts for the paucity of exposures. 



In a quarry north of Lower Court the beds are well seen, and 

 are very fossiliferous, having yielded specimens of all the species 

 mentioned in the foregoing list. The more arenaceous beds exhibit 

 the typical striping of the Didymograptus-Murcliisoni Beds. (These 

 beds are not exposed here, but are believed to be present immediately 

 north of the quarry.) The beds here dip northward at about 45°, 

 and appear to pass under the D.-Marchisoni and the D.-bifidus Beds 

 of Danrallt ; a fact which leads to the conclusion that the strata are 

 here upside down, by reason of the overfolding already referred to. 



North of Pant-dwfn there is another quarry in these deposits ; 

 but the dip is here a little west of south, and the beds are in 

 their normal position. This is, seemingly, the ouly fossil-locality 

 known to earlier writers. 



Immediately west of this quarry the beds are cut off by the fault 

 which brings the black Dicranograptus-Sh&les against Didymo- 

 graptiis-hifidus Beds near St. Clear's Bridge. The effects of this 

 fault are seen in several places between St. Clear's and C16g-y-fran, 

 where the Asaphus-Beds are again well exposed, in several quarries 

 which have, in years gone by, supplied much stone for lime-burning. 



