1:24 MESSES. JUKES-BROWNE AND SCANES ON THE [Feb. I9OI, 



There is, however, a possible way out of the difficulty. The 

 contemporaneous fauna of the top bed of the Upper Greensand in 

 Dorset is certainly similar to that of the Eye Hill Sand and the 

 phosphate-bed at Maiden Bradley ; but though fossils are abundant 

 therein, Ammonites varians is not common. Hence it is possible 

 that this bed is really the equivalent of the sand below the Cornstones 

 only, and that the gap in Dorset is represented in Wiltshire not 

 only by the Stauronema-hedy but also by the Cornstones and the sand 

 between them. If this be the case, the objection to the inclusion of 

 the Cornstones and the fossiliferous part of the Rye Hill Sand in the 

 zone of Ammonites varians would cease to exist. We propose to 

 make further examination of the Dorset sections in order to satisfy 

 ourselves on this point. 



Meantime, both in order to emphasize the importance of the 

 Rye Hill fauna, and to distinguish these beds from the rest of 

 the Selbornian Sands, we propose to group these debatable beds as 

 a distinct zone or sub-zone. Por this the Echinid Catopygus 

 columharius will serve as an appropriate index, since it is 

 especially abundant both at Rye Hill and Maiden Bradley as well 

 as in Dorset, while it is rarely found in the Chloritic Marl above. 



Where most complete, as at Rye Hill, this sub-zone consists of 

 three distinct beds, which, in descending order, are: — 



(3) Brownish sand, with many fossils, passing up into greenish-grey sand. 

 (2) A layer of calcareous concretions (the Cornstones). 

 (1) A greenish sand-rock, with calcareous concretions. 



The recognition of such a zone or sub-zone of Catopygus colum- 

 harius will be of service, because it will not only indicate the 

 existence of certain passage-beds in Southern Wiltshire, which form 

 an important factor in the complete sequence, but it will also enable 

 us to refer with greater precision to their correct horizon in the 

 series such portions of a less complete succession as occur in other 

 places. Thus we can say that, in Dorset, a part at least of the 

 sub-zone of Catopygus columharius is present, and it will be in- 

 teresting to ascertain whether there are any traces of the former 

 existence of this zone in the Isle of Wisrht. 



^O' 



The following is the sequence of beds which can be recognized 

 at the junction of the Selbornian and Cenomanian, where the 

 succession is complete : — 



4. Chalk-Marl. 



3. Sub-zone of Stauronema Carteri, 

 2. Sub-zone of Catopygus columharius. 

 1. Chert-Beds. 



