Vol. 51.] OF THE MID-COTTESWOLDS. 435 



In my former paper the length of time taken up in depositing 

 the ' Inferior Oolite ' was divided into 12 hemerae : now this is 

 increased to 13, with indications that yet more subdivisions may be 

 required. Of the exact correlation between the deposits in different 

 basins which can be made by the hemeral system I offer this paper 

 as evidence. 



It is now 35 years since Wright, in the conclusion of a paper read 

 before this Society, remarked L : — ' The existence of three different 

 faunas in the Inferior Oolite is evidence that a long period of time 

 elapsed during the accumulation of this formation.' How much more 

 strongly does the case stand to-day when it is seen that 13 different 

 faunae can be traced over a very considerable area ! I do not know 

 what estimate has usually been formed concerning the comparative 

 length of time required for the deposition of the ' Lias ' and the 

 ' Inferior Oolite ' respectively ; but seeing that when the latter was 

 divided into 3 zones the former was partitioned into 15, 2 the inference 

 is that the time for the former was 5 times as great. If the Lias 

 zones (stratigraphical divisions) be translated into hemerae (time- 

 divisions), then 15 hemerae for the ' Lias ' and 13 for the ' Inferior 

 Oolite ' would probably state the relative lengths of time more truly. 

 The ' Lias,' both at home and abroad, had certainly received very 

 much more attention than the Inferior Oolite, while it is fossiliferous 

 and ammonitiferous where the deposits are thick : it is not likely 

 that even minute work would require the division of Liassic time 

 into a much greater number of hemerae than of zones now recognized. 

 On the other hand, the great increase for the Inferior Oolite — from 

 3 to 13 divisions — is due to the fact that its beds are now receiving 

 attention more nearly equal to that formerly given to the Lias. 



That the Inferior Oolite only obtained 3 divisions in the first 

 place is due to this, that where its deposits are thickest and had been 

 most carefully investigated, they are frequently unfossiliferous and, 

 generally, non-ammonitiferous. At present, however, our knowledge 

 of the strata deposited during either of these epochs, ' Lias ' or 

 ' Oolite,' is, except in regard to a few favoured localities, very 

 incomplete ; while the majority of records are useless from want of 

 precision. If any estimate is to be formed of the comparative length 

 of time occupied in the deposition of ' Lias ' and ' Oolite,' or any 

 portions thereof, we require a knowledge of the various deposits 

 made during the different hemerae, and especially a knowledge of the 

 maximum thicknesses attained. It is partly as a contribution 

 towards this end — a very incomplete contribution, it is true — that 

 the present paper is offered. 



1 'Inferior Oolite,' Quart. Journ. Geol. Soc. vol. xvi. (1860) p. 48. 



2 Wright, 14 or 15 ; the number has varied considerably in both cases, but to 

 the ' Inferior Oolite ' has always been given far the fewer number of divisions. 



