390 J. F. BLAKE AND W. H. HTTDLESTON ON 



ley and Shotover limestones above it. It is thence continuous west- 

 ward, putting on various forms when it approaches Calne, including 

 the Calne and Goatacre freestones, and having underlying flags 

 near Purton. We cannot be sure of the age of the Westbrook Rag, 

 which contains no Cidaris jlorigemma. The true Rag is developed 

 again at Steeple Ashton ; at Westbury its place appears to be taken 

 by glauconitic sand. As a true Coral Rag it does not appear in the 

 North-Dorset district ; but its position in the series is indicated by 

 the rubbly beds, and possibly by the overlying calcareous sandstones 

 at Sturminster, and by slight coral-growths north of Gillingham. 

 In the Weymouth area the sequence is physically altogether dif- 

 ferent. 



6. The Supracoralline Beds. — We may use this name for the 

 uppermost portion of the series, in spite of the exceptional small 

 reef in Ringstead Bay. Omitting this, we may describe them as con- 

 sisting of calcareous grits and clays, and consider them as belonging 

 to two separate divisions. First and lowest are the Sandsfoot clays 

 and grits, which appear to represent beds deposited between the epoch 

 of the Coral-Rag deposits and the ordinary Upper Calcareous Grit of 

 most other localities, having in some respects a highly Kimmeridgian 

 fauna, but also a great and marked community of forms with the 

 Rag ; second and highest, the Upper Calcareous Grit of Yorkshire, 

 which is local even there. It is essentially a Kimmeridge forma- 

 tion. It is represented by more argillaceous beds in the Howardian 

 Hills. It has representatives in the red ferruginous marls with 

 oolitic fragments, and the sands which overlie the Rag from Faring- 

 don westwards to near Goatacre. To this horizon we assign the 

 Westbury ironstone and the red marls at the top of the series in 

 the North-Dorset district. In the Weymouth area we must look 

 for this horizon above the Sandsfoot grits, in the beds which in- 

 tervene between them and the Kimmeridge passage-beds, possibly 

 including the latter. Here, also, belongs the Ringstead reef, 

 and certainly the Abbotsbury ironstone, which may be even of 

 somewhat later order in the series. We cannot, therefore, correlate 

 what might be called the Upper Calcareous Grit of Weymouth with 

 that of Yorkshire, the former representing a lower portion of the 

 series. 



In this arrangement of the beds in series we are of course assisted 

 by their palaeontology ; but, with the exception of Cidaris Jlori- 

 gemma, we have scarcely ventured to use fossils as universally 

 characteristic of different portions. It will be well, however, to 

 name some which are generally of use for this purpose. Ammonites 

 perarmatus may be taken as an indication of something below the 

 Coralline Oolite ; yet it or one undistinguishable from it has occurred 

 in the representative of the Rag at Sike Gate. Avicula ovalis and 

 Millericrinus echinatus indicate the same portion. Gervillia avicu- 

 loides in Yorkshire indicates a low horizon, but in the south of 

 England generally a high one. Rliynchonetta Thurmanni belongs 

 to the two lowest series in Yorkshire, but does not occur there in 

 the south. 



