it4 



NATURE 



\pec. 7, 187 



with which they are specially concerned to the life of the 

 period which followed it. 



A dispute of a similar nature arises when we come to 

 the boundary between the Lower and the Middle Lias. 

 The tabulated lists of fossils given by our authors show in 

 the Yorkshire area a marked palaeontological break 

 between the zones of Ammonites oxynotus and A. 

 Jamesom, and a similar break has been observed at a 

 corresponding horizon both elsewhere in England and 

 on the Continent, Here then German and a large 

 number of English geologists draw the line. But a diffi- 

 culty arises when we attempt to construct maps accord- 

 ing to this classification ; unfortunately the marked 

 change in life is not accompanied by a corresponding 

 change in the character of the rocks ; the beds above and 

 below the palaeontological line are lithologically so much 

 alike that it would be impossible to separate them on a 

 map by the ordinary methods of geological surveying. 

 Somewhat higher in the series, however, a change in 

 lithological character, marked and sudden enough to 

 allow of its being traced with considerable accuracy, does 

 occur, and the field geologist, finding that he can sepa- 

 i-ate on his map the rocks above and belov this line, 

 naturally draws a boundary here. Hence it arises that 

 the subdivisions drawn on maps, such as those of the 

 Geological Survey, do not coincide with those established 

 from palaiontological considerations. And no harm 

 would follow from this if the lithological line always kept 

 the same place in the series ; we should merely have to 

 bear in mind that the boundary laid down on the map 

 was adopted out of sheer necessity, because it was the 

 only line that could be traced, that it did not coincide with 

 any great change in life, but that the palasontological 

 break occurred at a certain distance below it. But in the 

 case before us the hard sandstones and ironstones of the 

 Middle Lias are notoriously irregular and uncertain, and 

 if we make the Middle Lias begin where rocks like these 

 — which can be separated on a map from the clays— first 

 make their appearance, we shall place in the Lower Lias 

 at Banbury beds which we call Middle Lias at Frod- 

 ingham. In such a case, when the map-maker is driven 

 to neglect or set at defiance palaeontological boundaries, 

 the right thing would seem to be that he should call his 

 sub-divisions by names different from those used by the 

 palaeontologist ; on the Survey maps, for instance, it 

 would be better to drop the terms Lower, Middle, and 

 Upper Lias, and speak merely of Lias Clays, Sandstones, 

 and Ironstones, leaving it to the palaeontologist to decide 

 to which of the three sub-divisions the strata distinguished 

 on the map ought in each locality to be assigned. It 

 should be added, however, that Mr. Judd has something 

 to say even from a palseontological point of view for the 

 classification of the Geological Survey ; ^ though it must 

 be confessed that his words sound somewhat as if he 

 were dutifully trying to make the best case for a line 

 which his official position rather than his own convictions 

 led him to adopt. 



For the painstaking zeal with which the authors have 

 in succeeding chapters worked out the palaeontology of 

 the different minor sub-divisions, and described the loca- 

 lities where each may be studied, and for their long and 

 elaborate descriptions and figures of the fossils the thanks 



• "Th« Geolojfy of Rutland" (Memoirs of the Geological Survey), p. 45. 



of all geologists, and specially of those interested in tli 

 district, will be gratefully rendered ; and as they ha\ 

 thought it necessary to defend the minute and detaile 

 character of their work, a word miy be added 

 this head. It is somewhat unfortunate that a specii 

 term, "zones," has been applied to those lesser sul 

 divisions, which in common with the majority of pala 

 ontologists they have sought to establish. It leads 1 

 the notion that a " zone " is something different from 

 " formation," and to a vague fear that the zone-maker 

 introducing some new and presumably unsafe method inl 

 geological classification. But if, as the evidence seems t 

 show, each zone is characterised not indeed by fossi 

 entirely peculiar to itself, but by certain assemblages ( 

 fossils which are not met with in any other zon 

 then the principle on which zones are establish^ 

 is identically the same with that which determines tl 

 larger sub-divisions, and the only difference between 

 zone and a formation is that the one requires more cai 

 and labour to detect and defiue ic than the other. / 

 our authors remark, we are quite in the dark as to t 

 causes that brought about the change from the fauna i 

 one zone to that of the succeeding zone ; but just tl 

 same remark applies in many cases to the more marke 

 differences between the fauna of successive formation 

 If, then, the palzeontological facts on which zones ai 

 based can be securely established, the existence of thes 

 minor sub -divisions is a fact which geologists cannot refui 

 to recognise ; but it is just here that the rub occurs. Tl 

 intolerable complexity and uncertainty of palseontologic 

 nomenclature, the utter want of agreement on points < 

 the first importance between many leading palaeontoL 

 gists, the strong tendency which so often exists to a mu 

 tiplication of species in order to justify existing sul 

 divisions or even tj increase their number, have raise 

 suspicions and distrust in pateontological grouping, ui 

 founded perhaps, but for which palceontologists ha\ 

 only themselves to thank. What can, for instance, t 

 more monstrous than the idea that the time at which 

 lived ought to be taken into account in the definition ( 

 a species ? An idea which, according to one of 01 

 authors, only a limited number of palaeontologists ai 

 prepared to repudiate. If you have two creatures exact 

 alike in every respect, what reason can there be for cal 

 ing them by different names because one is alive now an 

 the other died ages ago ? The idea is closely akin to tl 

 old superstition that the volcanic rocks of the earli( 

 periods must have been different from thDse of the preset 

 day, and that if no real difference can be detected b( 

 tween them, they at least ought to be called by differei 

 names. Such a notion is now scouted by the mo; 

 advanced petrologists, and when palaeontologists follow i 

 their steps, they may be assured that the objections whic 

 some geologists have urged against their smaller and les 

 easily recognised sub- divisions will no longer be heard. 

 We cannot help thinking that the authors have lai 

 rather too much stress on the littoral character of tli 

 Lias in the northern part of the North Riding. The 

 lean to the conclusion that the Lias never extended muc 

 further towards the north-west than the points where w 

 now last see it in that direction ; in fact one or two c 

 their expressions seem to hint that the Lias of the Nort 

 Riding was deposited in a basin of its own. This ca 



