1922 CHRONOLOGY 17 



are several penecontemporaneous erosions, \nth consequent absence of 

 beds — non-sequences . 



It is doubtful if any ammonitiferous strata of these Ages occur on 

 the Continent, except at Boulogne, France. There the Ammonite-fauna 

 of the Paravirgatitan Age can be recognized, but it is doubtful if anything 

 indicates Behemothan date : the fauna of the early hemerse of Gigantitan 

 date may be present — in the species, " Perisphinctes" gorei and Am. 

 hononiensis ; but neither of these has yet been satisfactorily matched 

 by specimens from this district. There is nothing to correspond with 

 the Ammonite-fauna of the later hemerae of the Gigantitan Age, with 

 Titanites, Briareites, and other giants. 



Further afield there seems to be nothing to correspond with the 

 Behemothan nor with the Gigantitan faunas. The Indian Virgato- 

 sphindes looks as if it should be about of Paravirgatitan date. The 

 Tithonian, usually dated as Portlandian, is mainly of Aulacospkindean 

 date — Psev.dovirgatites indicating perhaps something a little later. It is 

 possible that between the Gravesian and Behemothan Ages more Age- 

 names will have to be introduced to form a satisfactory chronology : 

 possibly the European strata lack much — have many great non-sequences. 



There is trouble with the \'irgatitan Age. Its position is in 

 accordance with the dicta of Pavlow, Salfeld, and others, who have 

 correlated the Hartwell Clay and, perhaps, locally, some Portland Sands 

 with the Virgatites Beds (Lower \'olgian) of Russia. But the peculiar 

 virgatome ribbing of the Russian Ammonites would appear to be wholly 

 lacking from English specimens, so their identification with Russian 

 forms is much suspect. It would not be surprising to find that the 

 Mrgatitan Age (Lower \'olgian) is of far later date — perhaps later than 

 Gigantitan. Hence, ^'irgatitan Age in the Table is marked with a 

 quer\' and Pseudovirgatitan is suggested as possibly a more correct 

 alternative. 



Mr. J. Pringle has shown me a specimen from the oil-shales of 

 Kimmeridge, Dorset, which he suggests is Pseudovirgatites scruposus 

 (Oppel) \'etters. See also H. Salfeld, p. 208. This would correlate the 

 oil-shale horizon of the Kimmeridgian of Dorset with one horizon of the 

 Tithonian of Austria. No such form has been found in the Hartwell 

 Clay ; so presumably Hartwell is of slightly different date, later. 



Other names of Ages are marked with a query, to express some 

 uncertainty about their fauna, or their position, or their value. 



Like the wide geographical failure of the deposits of Gigantitan Age 

 is the failure of part of the deposit of Zigzagiceratan Age ; — only the 

 failure, if not so prolonged in regard to time, is remarkabh- pronounced 

 at a certain date. The large Zigzagiceratids (Z. poll u brum, CCLIX 

 Z. rliahdoi'.chits, CCC, and other species) are only known in England at 

 two localities in Dorset and at one in Somerset : Continental literature 

 gives no sign of them, though the small zigzag forms are quite widely 

 distributed. 



Quite the opposite to this appears at first sight to be the case with 

 deposits of the Macrocephalitan Age — Macrocephalites is recorded from 

 all over the globe, apparently indicating widespread synchronous deposits, 

 which did not suffer denudation. But all this ma\- be an illusion. 

 Analysis of the Macrocephalite faunas and deposits has not been carried 

 far enough yet ; but it has been done sufficient^ to show that Macro- 

 cephaUte-bearing beds are anisidophorous, and so not synchronous. 

 There is promise of some half-dozen different horizons in the deposits 

 of the Macrocephalitan Age in England : there is a suspicion that the 

 geographical preservation of some of these deposits is very limited in 



