A. J. Jukes- Browne — Zones and Mcqjs. 217 



The mistaken ideas prevalent between 1860 and 1870 respecting 

 zones are reflected by Mr, C. Moore, who makes some observations 

 on the " value of zones of zoological life," which show that he 

 thought the fauna of a zone was supposed to be strictly con6ned 

 to it, and he indicates some exceptions to the supposed law.' 



Professor Phillips seems to have regarded zones as relating to the 

 succession of species belonging to some single order or class ; thus, 

 after referring to the useful results obtained from a study of 

 ' Ammonite zones,' he says : " the same method .... ought 

 to be applied in all cases of large groups ; we should have zones 

 of Echinodermata, Brachiopoda, etc., treated independently of the 

 Cephalopoda, with which they would not necessarily synchronize, 

 and finally all would be combined into a true system of geological 

 chronology."^ No doubt such a study would be very useful, but tlie 

 idea of a zone conveyed by Phillips is not that held and expressed 

 by those who were then actually working at zones ; it does not even 

 imply a zonal fauna, much less a set of strata identified by such 

 a fauna. 



In an earlier publication, however, Phillips seems to have used 

 the term zone in a sense which approaches more closely to its 

 normal signification. He says :^ "A palaeontologist finds the whole 

 Carboniferous Period one, though in it are several zones distinguish- 

 able by the prevalence of a few types and by the paucity or absence 

 of others." 



It is evident that the men of Phillips' generation were not 

 consistent in their use of the term zone, and that few of them 

 had seen the necessity of formulating a clear definition. Since 

 1880 this necessity has been more felt, and the value of the zonal 

 method has been nun-e fully recognized. In some quai'ters, however, 

 there is still a lurking antagonism to it, and a disposition to regard 

 it as a method which is based on a different principle from that 

 which guides ordinary stratigraphical work. I hope, however, to 

 show in the sequel that this is a mistake. 



It is curious to find Mr. H. B. Woodward so late as 1892 defining 

 a zone in a zoological and not a stratigraphical sense, and stating 

 that " zones are assemblages of organic remains, of which one 

 abundant and characteristic form is chosen as an index," though 

 in a later paragraph he remarks that " the essential idea of a zone 

 is that it marks a period of time."* It is quite true that one 

 essential idea of a zone is that it corresponds to a period of time, but 

 if so, it seems to me that it must also correspond with the depth of 

 sediment formed during that period. This sediment, of course, will 

 vary in depth and character from place to place, but it unquestion- 

 ably forms a baud or zone of sedimentary material, and it must be, 

 to say the least, as correct to define a zone as a band of stratified 

 rock as to call it an assemblage of fossils. This is certainly the view 

 taken by most recent writers. 



' Quart. Journ. Geol. Soc, vol. xxiii, p. 510. 



2 " Geology of Oxford," 1879, p. 132. 



^ Quart. Journ. Geol. Soc, vol. xvi (1860), Pres. Add., p. xxxviii. 



* " On Geological Zones " : Proc. Geol. Assoc, vol. xii, p. 298. 



