MR. H. B. WOODWARD ON A WELL-SIXKING AT SWINDON. 295 



forms maintained, even if the species are not limited to the often rigid 

 and therefore unnatural definitions of a zone. 



Thus in the upper 288 feet, Ammonites cordatus and A. cordatus 

 var. excavatiLS are met w\i\i. This division would therefore corre- 

 spond with the " cordatus-clays," although the two Ammonites 

 occur a little lower down together with other species. 



In the next 220 feet, A. crenatus, A. Duncani, A. Jason, A. 

 Kosnigi, A. LamOerti, A. JIarice, and A. plicatilis occur. And this 

 division no doubt represents the " ornatus-clays " of the Lower 

 Oxfordian. In the next 18 feet we find A. Jason, yslt. Gulielmi, and 

 A. calloviensis. The lowest 44 feet, comprising alternations of 

 clays, sands, and sandstones, yielded A. Koenigi, A. Bakerice, and 

 A. modiolaris, found also higher up ; likewise A. Gowerianus. The 

 last-named two species are usually regarded as Callovian forms. 



Gryphcea dilatata occurs over 500 feet down in the Oxford Clay. 

 This fossil is especially common in the upper part of the formation, 

 in brickyards near the junction with the Corallian rocks in the 

 south-west of England. A small form, difficult to distinguish from 

 G. bilobata, however, occurs lower down, even in the KeUaways 

 Rock. 



The development of sandy beds at the base of the Oxford Clay is 

 interesting. On lithological evidence, about 44 feet may be assigned 

 to the Kellaways Rock ; but if we consider Ammonites calloviensis 

 to belong exclusively to this rock, then at least 18 feet more may be 

 grouped with the KeUaways division. The evidence, however, 

 agrees with that furnished in other localities, that the KeUaways 

 Rock is but an irregular and impersistent sandy basement-bed of the 

 Oxford Clay, locaUy fossiliferous. 



So far as I am aware, no good sections of Kellaways Rock are now 

 to be seen near the viUage of Kellaways. The beds, consisting of 

 fossiliferous and somewhat flaggy calcareous sandstone, are exposed 

 beneath the Alluvium of the Avon, about half a mile below Kella- 

 ways Bridge ; and both here and at Christian Malford, where the 

 rock has also been observed, this fossiliferous horizon is probably 

 some distance above the base of the Oxford Clay. At the latter 

 locality the section was described by Lonsdale as follows : — 



Clay. ft. in. 



Rotten rubbly stone with few organic remains 5 



Sandstone, abounding with fossils , 3 



Sand 4 



Clay. 



The rock at KeUaways attracted the attention of WiUiam Smith, 

 on account of the numerous organic remains in it, for the fossils are 

 sometimes so numerous as to constitute nearly the whole of the 

 stratum ; but, as Lonsdale has remarked, they are often wanting*. 



Near Trowbridge bands of sandstone are occasionally to be seen 

 in brickyards opened in the lower beds of the Oxford Clay t. 



* Trans. Geol. Sec. ser. 2, vol iii. p. 261. 



t See R. N. Mantell, Quart. Journ. Geol. Soc. vol. vi. p. 312. 



Q. J. G. S. No. 167. Y 



