2Cji Ocohgical Society. 



These, with the Domerian, each contaui on an average about 

 ten hemerje, the grouping being controlled bv the dominance of 

 ammonite families or phases thereof — thus, Domerian : Age of 

 Amaltheids ; Raasayan : Age of Deroceratidte and Echioceratid;e. 

 It is obvious that, with this increase in the number of hemerae, 

 the number of local non-sequences is greatly inci'eased. Some 

 comparative diagrams illustrate this. 



One of the most intei-esting discoveries which has resulted, partly 

 from the great thickness of Scottish strata investigated and col- 

 lected from, partlv from compai'isons with other areas, is that the 

 so-called ' annafum Zone' of the English Midlands and that of 

 the Radstoek district, of Yorkshire and of the Scottish Isles, are 

 not isochronous, but are separated by a time-interval which cor- 

 responds to a thickness of some 300 feet of deposit in the Scottish 

 area. Thus, instead of the simple descending sequence 



Deroceras armatum 

 Echioceras raricostatum, 



there is this sequence ascertained : 



An upper Deroceras horizon, 



An upper Echioceras horizon in three distinct stages, 



A 10i\-er Deroceras horizon, 



A lower Echioceras horizon with some Armatoids ; 



and even now possibly this is not the end of the complication. 

 This alternation of Deroceras and Ecliioceras involves a pheno- 

 menon which the Author calls ' faunal repetition,' and it is a 

 reasonable supposition that this is not a solitary case — that is to 

 say, doubt is at once thrown on the contemporaneity of other so- 

 called * zones ' where they have been determined in different areas by 

 the j)resence of certain species of a genus — the species admitt<?dly 

 not the same — or by the alleged presence of a single species on 

 specific determination insufficiently rigid. The cases of zones 

 determined on the lucus a non Jucendo principle — the sti-ata in 

 c.oiTect intermediate position, but with the index zonal species 

 conspicuously absent — seem esijeciaUy to invite scepticism. 



Three appendices are given — one, palajontological, containing 

 descriptions of certain notable species, mostly new ; another, his- 

 torical, containing notes on certain ammonites described and figured 

 by "Wright in a paper published some years prior to the issue of 

 his Monograph : it affords clues to the interpretation of his 

 species, to the recognition of some of his missing types, to the 

 identity of certain figures in Reynes's Monograph, and to the geo- 

 graphical disti'ibution of species — a matter of particular importance 

 in regard to faunal dissimilarity ; the third, geological, — a com- 

 munication by Mr. J. W. Tutcher, embodying his reading of the 

 sequence in the lower part of the Lower Lias carried down to the 

 base of the Hettanarian. 



