i6 TYPE AMMOMTES—IV Jmte 



Thus the following scheme may be suggested : — 



Virgatal Epoch — Craspeditan-Pseudovirgatitan . 

 Planulatal Epoch — Aulacosphinctean-Proplanulitan. 

 Coronatal Epoch — Macrocephalitan-Sonninian. 

 Falcif eral Epoch — Ludwigian- Amaltheian . 

 Capricornal Epoch — ^Liparoceratan-Deroceratan. 

 Arietal Epoch — Oxynoticeratan-Coroniceratan, 

 or to Caloceratan, if that Age be not claimed for the Ceratitoidic Period. 

 The Virgatal Epoch is parted from the Planulatal as the time of 

 more or less virgatome ribbing, shown in Pseudovirgatites and Virgato- 

 sphmctes besides Virgatites, and suggested by inner whorls of Para- 

 virgatites (PI. CCCVI). There is reason to suppose that the giants of 

 the Gigantitan-Behemothan Ages are descendants of virgatomes — the 

 change is shown in Paravirgatites. 



In regard to the columns of Table I : in column \a various new 

 terms, like Upper, Middle and Lower Cornbrash have been introduced, 

 for the sake of clearness ; but these will be justified in the hemeral 

 sequence. In column \b are given the usual stratigraphical terms 

 employed by English geologists, but these have varied greatly in their 

 application, changing with the lithic facies. In column it are the 

 stage-names usually found in Englisli text-books ; column III contains 

 some of the Continental stage-names, but their exact correlation with 

 the Stratal terms or with the Chronological terms is not to be insisted 

 upon : they have varied in their application according as the lithic series 

 of different localities have influenced the views of different authors ; 

 column IV shows the terms employed for Stages or Ages in the earlier 

 portions of this work and in the author's papers on Jurassic Chronology ; 

 wliile the last column presents the presumed sequence of the chronological 

 terms now proposed for the Ages. 



A few words on these are required. There are 43 Ages : 23 are 

 represented in this work up to Part xxxiii In' iigm-es of the name- 

 genus (ref. Roman large caps.), 8 by a form of the date, but not the 

 name-genus (ref. Roman small caps.), and 12 are not yet illustrated. 



The time of the Proniceratan Age is doubtful : it is here suggested 

 as occupying the time of the non-sequence between Portland and Purbeck 

 Beds. The species of " Perisphinctes " figured by Neumayr and Uhlig 

 from the ironstone of Salzgitter, Hanover (Ililsbild. Palaeontogr. N.F. 

 VII (3), 1881, pp. 135-203) may be of approximately the same date — 

 perhaps derived, perhaps entombed in a condensed deposit. 



The largest area of exposed Portland Rocks in England, if not in 

 the world, is found in the district East Oxfordshire — West Buckingham- 

 shire, in about the middle of which this work has been and is being- 

 written. It is rich in Ammonites, many are large, some are giants — 

 megalomorphs. The strata arc divided into some twenty beds by the 

 quarrymen, some of which show signs of redeposition. There are 

 certainly quite twenty hemene to be dealt witli, and if there be only 

 an average of two species to each hemera, that means forty species of 

 Ammonites for (Upper) Portlandian : more may be expected. 

 A summary of the strata is as follows : — 



rUpper Chalky J'eds (" Witchett " +). 

 (iigantitan Age < Sandstone {^Liiaiiiics, Briareites). 

 I Lower Chalky Beds {Gigantites). 

 (Speckled Beds and Sands. 

 Jjcluinothan Age <! (ilauconitic Marls [Lcucopetritcs). 



l^Cilauconitic Stone [Bchcmotli, (JlaitcolUJiites). 

 The apportionment between the Ages is provisional. Locally, there 



