Vol. 69.] THE 'KBLLOWAT ROCK ' OL' SCARBOROUGH. 161 



only developed locally so far as certain of its beds are concerned, 

 and that even within the county itself it passes laterally into, 

 and is contemporaneous with, the Oxford Clay. 



The idea that the Kellaways Rock and the Oxford Clay were 

 always and wholly sequential deposits, carried out in our literature 

 and in the museum arrangement of specimens, 1 where the same 

 species are found in a lower case headed ' Kellaways Rock ' and 

 in a higher case labelled ' Oxford Clay,' is one which must be 

 abandoned. These stratigraphical terms are misleading : they do 

 not indicate sequential deposits, but beds which were iu the main 

 contemporaneous. All that they indicate is the lateral change 

 from arenaceous or calcareous to argillaceous conditions. 



It is suggested that for the earlier deposits the term ' Callovian' 

 be retained ; the Callovian will then roughly coincide with the 

 development of the genus Cosmoceras and its allies Kepphrites 

 and Sir/aloceras. For the later deposits the term 'Divesian' (Dives, 

 Calvados) has been suggested to me by Prof. Welsch ; it marks the 

 development of Quenstedtoceras. When Qaenstedtoceras is replaced 

 by Cardioceras (Lower Calcareous Grit, Coral Rag, and, perhaps 

 in some cases, highest layer of Oxford Clay) the term should be 

 ' Argovian' for Carc/tocer«s-yielding strata following Divesian. 



These terms would be uniform ; but the terms ' Oxford Clay,' 

 ' Kellaways Rock,' etc., are useful, if it be remembered that they 

 vary in value in different localities. 



It is inadvisable to use 'Oxfordian' for Divesian, because in 

 Continental usage 'Oxfordian' stands mainly for Argovian (Oxford 

 Oolites). 



The suggestion illustrated in Table IV is that the Callovian- 

 Divesian deposits are locally incomplete ; that the deposits of certain 

 hemerse have been locally removed by penecontemporaneous erosion, 

 as is usual with deposits of the Bajocian, Aalenian, etc. ; that a 

 full sequence of deposits can only be obtained by placing together 

 the developments of many localities ; and that, to express the entire 

 sequence, a full table of zonal or hemeral names, such as is now 

 given, is necessary. The object of a full table of hemeral names is 

 to obtain a true record of the sequence of ammonite faunas as a 

 necessary prelude to a study of their development. 



A theory of unrepresented zones may explain in part why the 

 ammonite fauna of certain beds is so peculiar to Yorkshire ; but in 

 other cases, where zones are represented, and yet there is distinctive 

 peculiarity, that explanation fails. It may then be necessary to 



1 Such statements have given much trouble : see J. F. Poinpeekj, ' Jur. 

 Fauna of Cape Flora' Norwegian North Polar Exped. vol. i (1900) No. 2, 

 p. 120. The Professor rightly judges that 'the Kellaways Rock and the 

 Oxford Clay [of English geologists] may be petrographicafly different facies 

 of faunistically corresponding strata'; but then he, adds, 'and in both the 

 Kellaways Kock (especially that of Yorkshire) and the Oxford Clay, the 

 different zones of the Callovian, as they may be observed on the Continent, 

 cannot be separated.' That statement is disputable : the Yorkshire specimens, 

 from their different matrices, are easily separable into zones in the study, and 

 that must be possible in the field. 



