On tlie Distribution of Productus httmerosus. 21 



Clitheroe district of Lancashire, namely, in the upper part of the 

 Caninia zone (Co)/ 



It is, therefore, evident that Productus sublcevis occurs abundantly 

 on two widely different levels in the Avonian, one in the Upper 

 Caninia Zone, the other at the top of the Lower Dihunojpliyllum 

 Zone. Dr. Wheelton Hind, in questioning Mr. Parsons's reference 

 of the humerosus beds of Leicestershire to Dj, and at the same time 

 affirming his own belief in a Caninia age for the humerosus beds of 

 Caldon Low, failed to take this view.^ 



Strong confirmation of the Dihunophyllum age of the Caldon 

 Low beds is now supplied by Mr. J. Wilfrid Jackson's discovery 

 of Productus humerosus in limestones of " Brachiopod Bed " type 

 in Dove Dale, only a few miles to the north-east of Caldon Low.* 



The " Brachiopod Beds " of North Staffordshire and Derbyshire 

 were described by me as an abnormal facies, and assigned to Do, 

 with the quahfying remark that they possibly encroach upon D^.* 

 They have long been accepted as " knoll-reef " deposits of D0-D3 

 age, paralleled by the upper or Cracoe knolls in the Clitheroe-Craven 

 region of Lancashire, and by the massif of Vise, in Belgium. It is, 

 however, most interesting to find in Mr. Jackson's account of the 

 occurrence of Productus humeros^is in Dove Dale, evidence which 

 definitely suggests that the " Brachiopod Bed " phase in the Mid- 

 lands ranges downwards into Dj. The limestones bearing Pr. 

 humerosus in Dove Dale are clearly of " knoll reef " type, both in 

 their faunal characteristics and in their lithic structure ; and the 

 top of Dj is at once suggested as their horizon by a consideration of 

 the humerosus beds of Leicestershire. It may be remarked that 

 if the humerosus beds of Dove Dale lie some 500 feet below the top 

 of the Carboniferous Limestone, as suggested in Mr. Jackson's 

 account of them, then their stratigraphical position corresponds 

 rather closely with that of the Di-D.^ boundary as roughly determined 

 in the Buxton-Longstone traverse of the Midland area.* 



In concluding this note I take the opportunity of expressing 

 the interest with which I am following Mr. J. W. Jackson's researches 

 in the western part of the Midland area, a tract which was most 

 inadequately studied by myself, and the hope that he will succeed 



1 "In the Franco-Belgian area the early, smooth form of Pr. sublcevis occurs 

 in a persistent band between Tournaisian and Visean. In the South-Western 

 Province this mutation is very rare ; it has, however, been recorded from the 

 C2 oolite of Burrington. In the Clitheroe area, the early Pr. sublcevis enters at 

 the top of Ci and forms a persistent band at the top of C2 (as in Belgium)." 

 (A. Vaughan, Quart. Journ. Geol. Soc, vol. Ixxi, 1915-17, p. 47.) 



2 Geol. Mag., 1918, p. 480. Dr. Hind quoted the occurrence of Cyrtina 

 septosa in the humerosus beds of Leicestershire as one indication of Caninia 

 age as against Di age, notwithstanding the fact that Cyrtina septosa occurs 

 in Di of Derbyshire and the South-Western Province, and characterizes 

 a persistent band in D^ of the North-Western Province. 



3 Geol. Mag., Vol. LVI, 1919, p. 335 and pp. 507-9. 

 ^ Quart. Journ. Geol. Soc, vol. Ixiv, 1908, pp. 47-50. 

 « Ibid., vol. Ixiv, 1908, p. 39, fig. 2. 



