Vol. 56.] THE LOWEE LUDLOW FORMATION. 415 



24. The Lower. Ludlow Formation and its Grai>tolite-Fauna. 

 By Miss Ethel M. II. Wood. (Communicated by Prof. C. 

 Lapworth, LL.D., F.It.S., F.G.S. Read March 21st, 1900.) 



[Plates XXV & XXVI.] 



Contents. 



Page 



I. Introduction 415 



II. Literature 417 



III. General Stratigraphy of the Lower Ludlow Formation ... 420 



IV. Description of Typical Districts 423 



(A) The Ludlow District. (General Map on p. 424.) 



(B) The Builth District. (General Map on p. 430.) 

 (0) The Long Mountain District. (Map, PL XXVI.) 

 (D) Supplementary Districts. 



V. General Summary 447 



VI. Paleontology 450 



(A) General Characters of the Graptolite Fauna. 



(B) Description of the Graptolite Species. 

 (G) Synonymy. 



I. Introduction. 



The Lower Ludlow Shales, which form the lowest section of the 

 Ludlow division of the Silurian System, are most typically developed 

 in the neighbourhood of the picturesque old town of Ludlow. It 

 was in this district that they were first defined and described by 

 Murchison. Lithologically, they are here essentially an argillaceous 

 group of strata, the lower and upper limits of which are well marked 

 by two distinct calcareous beds — the Wenlock Limestone below 

 and the Aymestry Limestone above. Palseontologically, the Lower 

 Ludlow Shales are rich in fossils : brachiopods, cephalopods, 

 Crustacea, and graptolites. 



When the Lower Ludlow Beds are followed from the Ludlow district 

 north-eastward along their line of strike as far as the valley of the 

 Severn, south-westward as far as Aymestry, and eastward as far as 

 the Malverns and Mayhill, they are seen to retain their lithological 

 characters unaltered, and the Wenlock and Aymestry Limestones 

 are both well developed. But when these beds are traced from the 

 typical area to the west and north-west, the limiting calcareous 

 strata dwindle away and eventually disappear, until, finally, the 

 Lower Ludlow Shales merge lithologically on the one hand into the 

 W T enlock Shales below, and on the other into the Upper Ludlow 

 Flags above. It is clearly impossible, therefore, in these westerly 

 districts to separate, on purely lithological grounds, the Lower 

 Ludlow Beds as a distinct group from the formations which overlie 

 and underlie them. 



The proofs that the Lower Ludlow Beds of Britain contain a 

 characteristic graptolite-fauna have been gradually accumulated by 

 the researches of Hopkinson, Lapworth, Watts, Marr, and Lake 

 (see pp. 418-19); and the evidences of the existence of a similar 



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