Highest Coal-measures of Durham. 209 



group of shells appears to mark a definite horizon in the Durham 

 Coalfield. 



Not much zonal collecting of the fossils has been done in the Coal- 

 measures of this district, but I have a fair number of bivalves, mostly 

 collected at different times from pitheaps, and the Newcastle Museum 

 also has a number of specimens. From these it is possible to 

 ascertain roughly the sequence of the "mussels" in the main Coal- 

 measures of Durham and Northumberland. 



Kirkby, in 1864, mentions the shell that occurs at Claxheugh as 

 Anthracomya acuta, a species which is now placed in the genus 

 Carbonicola, but he gives no description of it. 



I submitted some of the smaller Claxheugh shells to Mr. Bolton 

 who returned them to me labelled " Anthracomya minima stage of 

 A. Phillipsi", and he remarks in a letter, " I have been breaking up 

 the ironstone nodules you sent and am extremely interested to note 

 that they contain beautiful examples of A. minima, the intermediate 

 stage between A. Icevis var. scotica or 'spat' and the adult 

 A. Phillipsi" 



I am not sufficiently well acquainted with the mollusca of the 

 Coal-measures to be able to discuss whether Mr. Bolton's views on 

 the various growth stages of this shell are in every instance correct 

 or not. 



It is also very difficult on reading the various publications on the 

 question to determine whether or not A. Phillipsi represents a 

 distinct zone in the English Coal-measures, and its recorded 

 distribution offers some points that require further elucidation. 



In the North of England its horizon seems to be a well defined and 

 restricted one. In Yorkshire it is reported, so far as I can ascertain 

 from one locality only, 1 namely, from a cutting near Conisborough,in 

 a band of soft ironstone about two inches thick among clays and 

 sandstones underlying the Permian. In the Nottingham area 

 Messrs. Lamplugh and Gibson 3 say that "the range of the distinctive 

 species of the genus Anthracomya has not been definitely fixed but 

 A. Phillipsi occurs in the top beds of the middle Coal-measures at 

 Gedling", and Mr. R. D. Yernon informs us that A. Williamsoni 

 (Brown) invariably accompanies the roof shales of the "Top Hard 

 Coal". 



In the concealed coalfield of Yorkshire and Nottinghamshire its 

 horizon seems also to be a definite one where it has not occurred 

 below the Top Hard or Barnsley Coal, and is regarded as characteristic 

 of the Middle Coal-measures above that seam. 3 



Matters, however, in the South of England, are much less clear 

 and Mr. H. Bolton 4 states that " Anthracomya Phillipsi is equally 

 abundant in the lower Coal-measures of the Bristol district and in the 

 upper series of Radstock ". 



In the Kent Coalfield a similar uncertainty seems to prevail. 

 Mr. Bolton, referring to Anthracomya Icevis, A. Icevis, var. Scotica, 



1 H. Culpin & G. Grace, Naturalist, No. 577, February, 1905, p. 40. 



2 Geology of Nottingham (Geol. Surv. Mem.), 1910, p. 17. 



3 Walcot Gibson, Geol. Surv. Mem., 1913, p. 25. 



4 Q.J.G.S., vol. lxvii, No. 267, p. 329, 1913. 



DECADE VI. — VOL. VI. — NO. V. 14 



