Daviesiella llangoUensis hi DerhysJiire. 461 



agreed that the Lower-Middle Cambrian boundary can be determined 

 by a study of the stratigraphy. Since the broader stratigraphy of 

 a given bed is not so much a matter of opinion as of observation, 

 the only inference that can be drawn is that there are breaks of 

 more or less magnitude at both the top and bottom of the 

 formation. In interpreting these Dr. Walcott refuses to admit 

 the possibility of the recurrence in Middle Cambrian time of 

 surviving remnants of the Mesonacidae ; the writer sees in the 

 sudden introduction of new forms evidence far more dejjendable 

 than the ultimate extinction of the old. 



On the Occurrence of Daviesiella llangollensis (Dav.) 

 in Derbyshire, 



By J. Wilfrid Jackson, M.Sc, F.G.S., Assistant Keeper, 

 Manchester Museum. 



T^HE object of this paper is to deal more fully with the occurrence 

 -*- of Daviesiella lla.ngoUensis (Dav.) in the Carboniferous Lime- 

 stone of Derbyshire,^ and further to make some observations on 

 the sequence in the Midland area. In a later paj)er I hope to deal 

 with the horizon of the " Brachiopod Beds ". 



D. llangollensis was first noticed by me when making a traverse 

 of the type-section between Miller's Dale and Buxton some 

 years ago, but at the time fragmentary specimens only were 

 obtained. These were tentatively referred to the species and placed 

 on one side awaiting more perfect material. On subsequent visits 

 I obtained nimierous specimens, which proved to be quite typical 

 of the species in question. 



The locality where D. llangollensis occurs is situated in Wye 

 Dale, immediately at the foot of Topley Pike, about 3 miles 

 east of Buxton. The beds containing it are exposed in a small 

 roadside quarry at the entrance to Deep Dale, and consist mainly 

 of well-bedded, dark-coloured limestones, dolomitized in part. 

 Som,e hard, black, calcareous shale is also present. 



The species is most abundant in the bed forming the floor of the 

 quarry, and in the dolomitic bed immediately above, but it continues 

 sporadically through some of the overlying limestones. Up to 

 the present its vertical extent has not been ascertained. 



Several other fossils are present in these beds, but their imperfect 

 nature renders identification somewhat difficult. The following, 

 however, have been recognized : Syringopora sp., LitJiostrotion 

 martini (broken corallites), Seminula cf. ambigua (or globularis), and 

 Bellerophon sp. (imperfect cast). 



The Daviesiella beds form part of the lowest limestones visible 

 in the typical east-west section of Dr. T. F. Sibly.^ They are 



1 See record in Geol. Mag., Vol. LIX. 1922, p. 335. 



- Sibly, " Fauna! Succession in the Carboniferous Limestone (Ujiper 

 Avonian) of the Midland Area " : Q.J.G.S., vol. Ixiv, 1908, pp. 34-82. 



