ZONE OF AMMONITES PLANORBIS. 



57 



This section likewise settles a point which has been often discussed, namely, what is 

 the age of the Saurian beds of Somerset? It has been generally supposed that they 

 appertain to the same horizon as the lower Saurian beds at Lyme Regis ; this, however, 

 is a mistake, inasmuch as the Saurian beds at Street belong to the zone of Ammonites 

 planorbis, whilst the Saurian remains at Lyme Regis, on the contrary, are for the most 

 part found in and above the zone of Ammonites BucUandi. 



Worcestershire and Glouc ester si dre. — The Am-. 2^Janorhis, Ostrea, and lower Saurian 

 beds, so well developed at Street, are likewise found in different parts of Worcestershire 

 and Gloucestershire, where they present the same stratigraphical relations, and yield the 

 same organic remains. 



The neighbourhood of Tewkesbury affords several good exposures of the infra-ammonite 

 beds. I have obtained Ichthyosaurus tenuirostris, Conyb., and Ichihyosaunis intermedins, 

 Conyb., from a bed of light-coloured Lias at Haselgrove, near "the Folly;" and the late 

 Mr. Dudfield, of Tewkesbury, collected several very fine skeletons Ichthyosaurus tenui- 

 rostris, Conyb., /. intermedins, Conyb., and I communis ^\ Conyb., with bones of 

 Plesiosaurus Hawhinsii, at Brockeridge Common, and from similar beds at other localities 

 around Tewkesbury; and I possess several vertebrae oi Plesiosaurus rtiyosus, Owen, which 

 were obtained from a bed of White Lias at Woolridge, near Hartpury. 



The junction of the Lower Lias with the red marls of the Keuper in the Vale of 

 Gloucester is, in general, indicated by a low escarpment, facing the west. At Brockeridge 

 and Defford Commons this natural boundary is exceedingly well marked, and between 

 these two localities are several quarries which expose to a greater or less extent the beds 

 now under consideration. The presence of Ammonites planorhis in the upper strata of 

 several of these sections has enabled me to correlate the beds beneath with the cor- 

 responding strata at Street, in Somerset, and at Binton, Grafton, and Wilmcote, in 

 Warwickshire. 



8 



