278 ME. s. s. BrcKMAJ^- oif [vol. Ixxiii^. 



best results the label should give not onh" the name of the place, 

 but the exact exposure — the more detailed the better. Then the 

 sequence of dissimilar faunas can be ascertained, especially when 

 the exposures stretch across the line of strike. 



But, even with localities alone, much can be done by analysis 

 and comparison. 



Another lesson may be learnt — it has been taught that the 

 absence of the zone-species did not invalidate the placing of the 

 strata in such a zone, provided that the stratigraphical position was- 

 accordant : it was onl}^ a local peculiarity. Such an assumption 

 is now seen to be very unsafe : such cases must be looked ujDon with 

 considerable suspicion. Dissimilar faunas, of locomotive organisms 

 like Ammonites, in contiguous areas are products, not of zoological, 

 but of stratigraphical differences. There are zoological provinces ;. 

 but the absence of a southern fauna from a northern area may 

 raean less for difference of date than the absence of a northern 

 fauna from a southern area. Yet in the case of two areas in 

 approximately the same latitude, the absence from one of a fauna 

 well-developed at the other, both said to be on the same horizon, 

 may well cause doubt as to their contemporaneity. This is a true 

 case of dissimilar faunas. 



The need for a much more systematic and continuous palseon- 

 tological output and for fuller illustration of species is obvious 

 from this investigation, where much difficulty of interpretation is- 

 due to the uncertainty of unillusti-ated records. Such an investi- 

 gation as this is both hindered and hampered by the present con- 

 dition of palaeontology, which cannot keep pace with, — in fact, is- 

 continually falling behind, the discovery of new material. Such 

 palaiontological study requires very considerable time ; and the 

 facilities for its prosecution and publication seem to be inadequate. 



Finally, I take the whole responsibility for the interpretation s- 

 that I have placed on the information and evidence laid before me ; 

 it must not be thought that my informants necessarily concur in my 

 views. For any mistakes — and it is too much to expect freedom 

 from error — I shall be to blame ; but I will be grateful for any 

 facts which expose them. 



Appej^'dix I. The Zoxal Sequence ik^ the Lower Lias 

 (Lower Part). By J. W. Tutcher. 



(1) Introduction. 



The district of North Somerset and South Grioucestershire — 

 approximately that occupied by the Bristol Coalfields — has chiefly 

 come under my observation. In this district the Lias has been 

 thrown into a sei-ies of folds having, in the main, an east-to-west' 

 trend. These folds increase in intensitj^ from north to south, 

 becoming more marked as the Mendip Hills are approached. 

 Partial and rej^eated denudation of the Jurassic rocks has followed 



