Vol. 51.] OP THE MID-COTTESWOLDS. 433 



Another thing should be noticed — the continuation of the boundary- 

 lines makes them meet at a point south-west of Cranham Wood. 

 Now it is known that at Cranham "Wood the Bajocian erosion not 

 only cut through the ' intervening beds,' but even began to destroy 

 the Upper Freestone or Oolite Marl series, down nearly to the line 

 where Terebratula fimbria is fairly common It is obvious, too, 

 that at Cranham Wood was found the lowest point of the erosion ; 

 and therefore the meeting of these lines at this point is another 

 argument in favour of the Mount Surat-Leckhampton line being at 

 right angles to the trough eroded. 



Quite different is the state of affairs along the other line of 

 country, where both the boundary-lines would have had to be con- 

 tinued at a different angle — to make them accord with the fact of 

 there being not only total removal of the ' intervening beds,' but also 

 removal of some of the Upper Freestone at Cranham Wood. 



As to the date when all this denudation took place, it is possible 

 to fix it within very narrow limits. Using the chronological term 

 proposed in my former paper — hemera — it can be said that the denu- 

 dation was hardly likely to have commenced before the end of the 

 Witchellice hemera ; because strata of this hemera are found in the 

 district. The erosion must have gone on during the hemeraa which 

 elapsed between the Witchellice and the Qarantiance hemerae (the 

 latter was the time of the deposition of the Upper Trigonia-grit) ; 

 and it must have come to an end before the strata of the Garantiance 

 hemera were deposited, because the Upper Trigonia-grit is found 

 lying on the eroded surfaces, and the Upper Trigonia-grit rests 

 successively, according to. locality, on Upper Freestone, Lower 

 Trigonia-grit, etc., up to Witchellia-grit. Now, it was shown in my 

 former paper that the time which elapsed between the Witchellice 

 and Garantiance hemera? could be divided into the following 

 hemerae : — Sauzei, Humphriesiani, niortensis. Therefore this erosion 

 took place during some or all of those hemerae, because no strata of 

 those hemerae have yet been found in the Cotteswolds, and there are 

 certainly none in the district now under review. 1 



The comparison of the Cotteswold strata with those of Dorset 

 set forth in Table II. (p. 422) will bring this matter clearly before the 



1 Some years ago Mr. H. B. Woodward, F.G.S., kindly gave me a Stephano- 

 ceras collected by Prof. R. Tate from Rodborough, and identified as Ammonites 

 Humphriesianus. In his ' Lower Ool. Rocks,' Greol. Surv. Mem., Jurassic Rocks, 

 vol. iv. p. Ill (1894), "Woodward speaks of Prof. Tate's find as evidence for the 

 Humphriesianus-zone in the Cotteswolds ; but the species is no more like Hum- 

 phriesiamis than it is like pettus of the Middle Lias. So wide an use of the 

 name Humphriesianus would justify calling Middle Lias Humphriesianus-zone ; 

 but when the term 'Humphriesianus-zone' is used it means a restricted series 

 of beds deposited contemporaneously with the Ooronaten-Schichten of Quenstedt. 

 Stephanocerata occur in several beds besides the Coi'onaten-Schichten, and con- 

 sequently the finding of a Stcpihanoceras is no evidence for the Humphriesianus- 

 zone sensu stricto. No beds contemporaneous with the Coronaten-Schichten of 

 Quenstedt have been discovered as yet in the Cotteswolds. At Rodborough the 

 gap between beds 2 and 3 is very considerable. Other sections in the district 

 fill it in to a certain extent ; but even they do not show any beds of the Hum- 

 phriesianus-zone, much less, therefore, can Rodborough. 



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