1922 CHRONOLOGY 25 



Another case: in the south of France, the fauna of Perisphinctes 

 martelli-type is placed in the zone of Peltoceras transversarium ; in 

 Wurtemberg the latter zone contains Uttle or no evidence of the martelli 

 fauna ; in England the strata with the martelli-iaxLndi — giants like those 

 of the South of France — show no transversarium. Also, in England, 

 penecontemporaneous erosion in these strata is very pronounced, even 

 in two sides of the same small quarr}^ and, as between different quarries, 

 there is much stratal failure. Penecontemporaneous erosion might, 

 then, account well enough for any local faunal failure. So that the 

 question naturally arises whether that accounts for the faunal differences 

 between the distant places cited — whether the martelli and transversarium 

 faunas, though homotaxial, were truly isochronous. With such doubt 

 it is an assumption without e\*idence to date the English strata as 

 transversarium, or those of Wurtemberg as tnartelli : it seems preferable 

 to keep the records distinct, though it may involve an assumption as to 

 sequence. Similar stratigraphical position does not prove contem- 

 poraneity, nor does the occurrence of two faunas in one thin bed prove 

 their isochronism : this may become impossible to maintain in the face 

 of adverse e\'idence from amphfied deposits elsewhere. Thick deposits, 

 poor in species, may be more reliable chronological guides than thin 

 deposits which are rich. But the latter, in most cases, attract the 

 greater attention. 



Such are the methods of the hemeral tables now to be given — 

 the sequences of many hemerge must be regarded as supposititious, because 

 correlation of localities analyzed according to a very detailed method 

 is particularly difficult — in the case of condensed, polyhemeral beds, 

 whose amplified deposits are unknown, it is nearly impossible. But 

 some local stratal and faunal sequences will be given to show the data 

 used. 



WTien hemeral names are bracketed together, possible synchronism 

 is suggested, though the names are used because of peculiarities of 

 faunal distribution. When a name is marked by an asterisk, e\'idence 

 as to position in the sequence is not altogether satisfactory* — a case of 

 surmise. The phenomenon of faunal repetition makes correlation difficult, 

 and surmise possibly erroneous. 



To place the hemeral tables in sequence, it is necessary to begin 

 with the youngest deposits : this is the wrong method of writing, having 

 regard to development, but the only method of presentation for a page 

 read downwards. 



For the equivalents of the Craspeditan Age, Dr. Salfeld gives three 

 zones : — 



Craspedites nodiger 

 C. subditus 

 C. okensis 



The fauna of the middle one only is said to be found in Yorkshire. The 

 hemeral sequence has, presumabh-, been incompletely anal\-zed, and lies 

 rather beyond this work ; for the rest of the English deposits of 

 Craspeditan Age are lacustrine. 



Incomplete knowledge may be urged in the case of the deposits of 

 the Proniceratan Age — the sequence is, perhaps, to be found in scattered 

 deposits of different dates. But for the main of the rest of the Virgatal 

 Epoch, the follo\nng hemeral sequence and stratal succession may be 

 suggested : — 



