part 4] .ruR.issTc ciiROXOLO(H' : lijlS. 263 



rej)resentin_o- the so-called zones of armatum-raricostatiim, where 

 they disclose a quite unexpected sequence of events. Concerning- 

 the upper part of the Charinouthian they do not give much infor- 

 mation ; but here Mr. Lang's detailed researches on the Dorset 

 Coast come in. 



Owing to the number of faunal horizons disclosed by the English 

 and Scottish strata, it becomes necessary to divide the Char- 

 mouthian ; and it is at once noticeable that in the upper part the 

 Ammonite families Liparoceratidae and Polymorphidse are domi- 

 nant, in the lower part the families Deroceratida^ and Echiocera- 

 tidye. But such division into two parts would leave the upper 

 portion unduly large, while division into three parts gives better 

 balance. In the upper third the Liparoceratidfe are the dominant 

 feature with the Polymorphid^je subservient ; in the middle third 

 the position is precisely the reverse ; while in the 'lower third the 

 Deroceratidip and Echioceratida^ keep alternating in their domina- 

 tion. Therefore it is proposed to divide the Charmouthian into 

 three ages, named respective^ Hwiccian, Wessexian, and Raasayan. 

 These terms are governed as to their limits, not by stratigraphy, 

 but by faunal constituents ; and there should be no necessity to 

 change them if future discoveries show the advisability of small 

 additions to, or subtractions from, the stratigraphical units now 

 respectively assigned to them. 



Perhaps no author has proposed, and, in the light of present 

 knowledge, perhaps no author can propose stratigraphical or chrono- 

 logical terms with fixed limits : non-sequences and the progress of 

 palseontological discovery are against such results. Detailed in- 

 vestigation has often revealed that the upper and lower limits of a 

 ^iven stratigraphical term used by the same author really vary 

 from area to area to the extent of the deposits made during several 

 hemerse in each case. Then the limits require corresponding 

 adjustments ; but to alter the names whenever small adjustments 

 are made would produce a confusing multiplicity of terms for 

 what is substantially the same thing. It is too much to expect 

 that limits can be exactly fixed, even on the basis of dominance of 

 certain Ammonite families : future discoveries may spring surprises 

 on us. It is unlikely that the remarkable sequence disclosed at 

 Raasay (Eaasayan, p. 2o7) with the large adjustment which it 

 involves will be the only discovery of its kind. 



(1) Hwiccian. 



The lower scarp of the Cotteswolds and the outliers which stand 



as sentinels along the valle3's of ScA-ern and Avon in the counties 



of Grloucester and Worcester show some fine developments of 



strata earlier than the Domerian. The Hwiccas,! whose country 



^ ' The Hmccas . . . the people of Gloucester, Worcester, and part of Warwick 



the old Diocese of Worcester before Henry the Eighth formed the sees of 



Gloucester and Bristol. The Bishops' Dioceses are g-enerally the best guide* 

 to the boundaries of old principalities.' — (E. A. Freeman, ' Old Enghsh His- 

 tory ' 3rd ed. 1873, p. 82.) 



