INTRODUCTION. 



3 



The notion that the succession of strata all over the world must be upon the same plan 

 as that of the best studied, typical or most familiar district favours this difficulty ; and it 

 is most true that the Lias has been, from the applicability of the foregoing remarks, a 

 very debateable ground. 



The relation of the Bone-bed to the Trias ; the propriety of forming a Rhsetic series ; its 

 relation to the Trias and Lias ; the possibility of arranging the strata of the Lias in Zones of 

 Ammonite life ; the propriety of including the Liassic strata between the Keuper and the 

 Zone of Ammonites Bucklandi, or between the base of the Zone of Ammonites planorbis 

 and the Zone of Ammonites Bucklandi in a sub-group, calling it Infra-Lias ; the possibility 

 of separating the Zone o{ Ammonites BucHandi from the Zone Ammonites angulatus, and 

 the impropriety of distinguishing Zones of Cephalopoda, Insecta, Sauria, or Madreporaria 

 — all these have been points debated over and over again, and they will ever be so as 

 long as artificial distinctions are placed " en rapport " with nature. 



Nevertheless, carefully collected palaeontological data concerning the vertical range of 

 species are gradually deciding many of these questions, and with the effect of isolating 

 the palaeontologist more and more in his relations with the received classificatory geology. 



These remarks are made because it is necessary to give the various groups of species 

 of Madreporaria of the Lias places in some classification or other. It is impossible to 

 associate them with beds determinable on purely stratigraphical or mineralogical data ; 

 and it is equally impossible to include them in Zones of special life, for Cephalopoda and 

 Saurians are rarely in relation with Corals. The groups of Madreporaria have a general 

 relation to certain zones of life and to certain strata ; and if they are associated for the 

 sake of a necessary classification with certain Ammonite-Zones, it must be understood that 

 it is only an approximative classification, and that both the Ammonites and the Madre- 

 poraria may range out of their supposed restricted zone, or not even be represented in 

 certain portions of its area. 



If it be admitted that by a Zone of an Ammonite or of any other Mollusc the general 

 and usual vertical limit of the species is meant, all the difficulties thrown in the way of 

 the philosophical, but still artificial, separation of the Liassic series into Ammonite- 

 Zones vanish. 



Dr. Wright has elaborated this system in his ' Monograph of the Oolitic As- 

 teriadae,'^ and had his Zone of Ammonites angulatus been known to have been as well 

 developed in Glamorganshire and in Lincolnshire as it is in some of its most typical 

 districts in France, his arrangement would have met with sHght opposition. But the 

 endeavour to give definite horizons to and to correllate Saurian, Insect, Ostraa, Ammonite, 

 and Lima beds has resulted in the production of confusion instead of the reverse. 



Whether the principle of the arrangement in "Zones of Ammonites is admitted or not, 

 it is absolutely necessary that the foreign equivalents of our Liassic subdivisions should 



1 Pal. Soc. 



