part 1] JURASSIC CHRONOLOGY : LIAS. 65 



So far as II, f aunal failure, is concerned, there are two causes 

 for this phenomenon, — one that of stratal failure (I), and the other 

 that of dispersal failure (III). But it is obviously most unsafe 

 to postulate the latter, until certainty has been arrived at that the 

 former is not the cause. For, as the former (stratal failure) means 

 failure of the accompanying fauna in most cases — though some- 

 times the fauna is redeposited in a later bed — , the former is a 

 sufficient cause of the latter. As the former is a very common 

 phenomenon, it is obviously safer to assume it as the cause of 

 faunal failure rather than to lay it to dispersal failure — a pheno- 

 menon ahout which little is accurately known. Yet, judging by 

 recent writings, the tendency is to jump at the latter conclusion 

 as the cause of faunal failure. On this point a few words will be 

 said presently. 



Exposure failure (IV). — This would not occur in railway- 

 cuttings, but might occur in a series of quarries. It is obvious 

 in regard to some of the subsidiary excavations connected with the 

 railway from which fossils are recorded by Mr. Richardson. As 

 these records would hinder rather than help the result, I have 

 disregarded them in the present case. 



Collection failure (V) and arrangement failure (VI). 

 — The former might result from many causes — lack of time, in- 

 complete searching, inaccessibility of places, rarity of species or 

 specimens, inability to bring away large specimens : it is needless 

 to consider these and other possible factors in detail, as they would 

 be obvious to geologists ; it may be judged that some of them do 

 not apply in the present case. But the point to be made is that 

 collection failure, in the case of several exposures in a limited area, 

 should, if the species have been arranged in correct order, disclose 

 itself by abrupt local lacunae. On the other hand, if the species 

 have been arranged in incorrect order (arrangement failure) there 

 would obviously be many such local lacuna?. To attempt to 

 account for these as collection failure would be a reflection on the 

 collector. A few local lacuna? may be accounted for mainly as 

 collection failure ; many local lacuna? as, more likely, arrangement 

 failure. 



In regard to VII, nomenclature failure, that can present 

 itself in many ways and in varying degree. Faulty nomenclature 

 would produce arrangement failure ; lumping nomenclature — 

 attribution of the same name to different species occupying different 

 horizons — would produce local lacuna?. 



"With many of the unillustrated and uncritical records which 

 have appeared in geological literature it would be almost impossible 

 to attempt anything — at least without very liberal interpretation, 

 Avhich even then might be insufficient. But Mr. Richardson's 

 nomenclature is quite satisfactory : it is as good as could be 

 produced without a prolonged technical investigation, which no one 

 has yet carried out with these species. Translation in a few cases 

 with ; cf.', 'aff.', and so forth is ventured from experience in collect- 

 ing from similar spoil-heaps in other parts of Gloucestershire many 



Q. J. G. S. No. 301. i- 



