Yol. 51.] OF IHE MID-COTTESWOLDS. 439 



Paet III. 



The Chronological Sequence of the Brachiopod-faen^; in the 

 cotteswolds and in dorset. 



In the discussion to which my former paper gave rise it was 

 urged that the deposits of certain divisions (hemeras) could not be 

 followed in the Midlands. I see, however, no reason why this 

 should be the case. Of course, if fossil evidence be scanty the 

 difficulty of stating just what deposits were laid down during 

 particular hemerse becomes increasingly embarrassing — just as the 

 Cotteswolds require far more work for their investigation than Dorset, 

 added to greater natural difficulties of locomotion, except in regard 

 to a few favoured localities ; but it is only a question of more pro- 

 longed study. From other remarks which have been made to me, 

 it seems to be thought that an absence of ammonite-remains would 

 render the work impossible ; but this again is an incorrect assump- 

 tion. If ammonites be scarce, correlation must be accomplished more 

 or less indirectly. Thus the Midlands might be correlated with, say, 

 the Cotteswolds by means of their brachiopod or other fauna, and 

 then, the correlation of Cotteswold and Dorset deposits being known, 

 the exact correlation of the Midland beds would be apparent. But 

 if certain Midland localities and deposits yield only an occasional 

 ammonite, then the date of the ammonitiferous deposits would be 

 fixed directly, and the date of other non-aminonitiferous deposits 

 would be inferred from the fauna associated with the ammonites. 

 Thus the ammonites would be a direct medium of exchange, the 

 other fauna an indirect one. This is the plan which has largely 

 been pursued in the Cotteswolds. Once there has been a definite 

 and exact record of the ammonites which are associated with any 

 particular part of the fauna — say the brachiopod portion — appeal 

 need not be made to ammonites at all. 



Of course, in the first place, for correlation between Dorset and 

 Gloucestershire, ammonites are practically the only medium of 

 exchange, but when it was known that certain strata of the Chelten- 

 ham or Stroud districts were, by the evidence of ammonites which 

 they yielded, deposited during certain hemerae, then strata of other 

 Cotteswold localities, though not yielding any ammonites, could be 

 correlated with Dorset. First they can be correlated with the 

 Cheltenham or Stroud beds by means of their brachiopods, and then, 

 as those have been already correlated with Dorset, the strata of the 

 other localities may be compared therewith. For local Cotteswold 

 correlation the brachiopods are amply sufficient, if carefully collected. 

 They are not of quite so much value as ammonites for small divisions, 

 because generally their chronological range was more extensive ; 

 but it was sufficiently restricted in all cases to make them very good 

 indicators. 



These remarks also apply to other divisions of the fauna. 

 Gasteropoda or lamellibranchiata may be selected by those who have 

 studied them, and similar work might be done in the correlation of 



