84 SECTIONAL ADDRESSES. 



I think there can be no doubt as to the desirability of the use in 

 Yorkshire of the term Yoredale Series or Mr. Cosmo Johns' variant 

 Yoredalian. Its top must clearly be taken as the level of entry of the 

 Lancastrian fauna of Upper Carboniferous type defined by Bisat. 



As regards the level to take as the base of the Yoredalian, the difficulty 

 is increased by the uncertainty as to what significance is to be attached 

 to the expressions ' top of D.^ ' and ' top of D.,.' The top of D,^ in the 

 Settle paper is just below the Orionastrcea band (Simonstone limestone 

 level), while in the Southampton report the Orionastrcea band is the top 

 of D3 (or 'upper D.^ '). 



The level taken as the top of D.^ (and base of the Yoredalian) by Mr. 

 Johns is in the shale below the Hardraw limestone, which he says corre- 

 sponds exactly with the base of the Yoredale series as defined by Phillips, 

 and with the base of Bisat's zone P. I am informed, however, by Mr. 

 Hudson that the latter argument no longer holds, recent goniatite work 

 having shown that part of D.^ is to be correlated with lower P. The 

 chief argument in favour of Mr. Johns' proposal is the admitted con- 

 venience of the base of the Yoredalian coinciding with a well-marked 

 change in lithology, and with the base of the Yoredale series of Phillips. 



On the other hand the following facts tell in favour of the adoption of 

 the Orionastrcea level as the top of D.^ : — ■ 



1. It is a level having as a rule a well-marked palseontological character. 



2. If this level be adopted, D^ forms a subdivision of considerable 

 thickness and includes both the upper and lower Lonsdaleia beds, instead 

 of only the lower. 



3. This is the level adopted for the top of Dj in the two most important 

 papers published in recent years on the northern succession, viz., that on 

 the Carboniferous Succession in the North-west Province by Prof. 

 Garwood, and that on the Lower Carboniferous Succession in the Settle 

 district by Prof. Garwood and Miss Goodyear. 



4. The level appears to coincide with the horizon of important strati- 

 graphical events, such as the Derbyshire and Cracoe unconformities. 



In view of these facts, I think that, on the whole, the best course to 

 pursue is to commence the Yoredalian at the base of the Orionastrcea level 

 and to include all between that level and the Girvanella level in D.^. There 

 would then be no need to use the expression D., in Yorkshire and the 

 North-west Province. 



The chief argument for giving the Yoredalian the status of a major 

 division of the Avonian equivalent to the Tournaisian and Visean is its 

 thickness and importance in the North of England. If, however {vide 

 supra), the Yoredalian is to be reduced by including its upper portion in 

 the Lancastrian, the argument loses much of its force. As was pointed 

 out by the authors of the sub-reports, the Yoredalian is not sufficiently 

 marked off faunistically or otherwise to merit its recognition as a major 

 division. The fauna is essentially a D fauna, and, in spite of its thickness 

 and importance in the North, I think there is nothing for it but to group 

 it with the D beds. 



I do not feel capable of expressing an opinion as to the desirability or 

 otherwise of recognising the zone 0. The fact that Orionastrcea is found 



