216 MB. G. W. IAMPLUGH ON THE SPEETON SEKIES [May 1 896, 



state of affairs prevails, as the above discussion has indicated, not 

 in England only, but throughout the greater part of Europe, 

 and also in North America. Under such conditions there must 

 necessarily be much discussion and interchange of views before 

 a boundary of general application can be agreed upon. Nor is this 

 at all attainable except by some sacrifice in matters of local con- 

 venience. 



Thus, in the North of England there is no doubt that in spite of 

 the early-recognized and oft-discussed Jurassic affinities of the 

 Spilsby Sandstone fauna, 1 the field-geologist working independently 

 in that district would find the base of that deposit to afford by far the 

 most suitable line of demarcation between the systems. It is a 

 strongly- defined horizon, marking the termination of a period of 

 quiet and uniform sedimentation over the whole region, while above 

 it, owing to more local and less stable conditions, the character of 

 the accumulation frequently alters horizontally as well as vertically, 

 thereby rendering the tracing-out of a synchronal line a matter of 

 extreme difficulty. Yet it seems inevitable that, in spite of its con- 

 venience, this line will have to be abandoned whenever the wider 

 bearings of the stratigraphy of the region are in question, unless 

 we are prepared to advocate extensive alterations in other areas to 

 suit it. If, on the other hand, we take the upper boundary of the 

 lateralis-zone as our line of division, we find that though in York- 

 shire, as Leckenby pointed out, this horizon is lithologically well 

 defined, in Lincolnshire, as already shown, in the southern part of 

 its course it is purely palseontological and scarcely traceable on the 

 ground. 



The division of the Zone of Belemnites lateralis into two portions- 

 by means of the ammonites, as proposed by Pavlow, suggests the 

 possibility of an alternative course, by which the lower part with 

 Ammonites subditus, corresponding to the major portion of the Spilsby 

 Sandstone and presumably to Beds D 5 to D 8 of Speeton, might 

 be separated from the rest of the zone, in which occur the ' gravesi- 

 form ' ammonites, and the one classed as Jurassic and the other as 

 Cretaceous. [This scheme is powerfully advocated by Prof. Pavlow 

 in his recent contribution to the Society.] But while this plan 

 would possibly satisfy some of the objections which have been raised 

 to the inclusion of the whole zone in the Jurassic, it appears to 

 me that the life-forms other than the cephalopoda common to the 

 two parts of the zone will, when fully worked out, be found so 

 numerous that a line drawn at this horizon would in England be 

 both palaeontologically and stratigraphically weak, without serving 

 the general European convenience better than before. 



1 Prof. H. G. Seeley, in the discussion on J. F. Blake's 'Portland Kocks of 

 England,' Quart. Journ. Geol. Soc. vol. xxxvi. (1880) p. 236, and in several 

 earlier discussions on similar subjects. 



Mr. G. Sharman, in Geol. Surv. Mem. 1887, ' East Lincolnshire,' p. 141,. 

 in discussing the fossils, remarks: — 'It is tolerably evident, therefore, that 

 these calcareous concretions (of the Spilsby Sandstone) occupy a lower horizon 

 han any Neocomian beds hitherto described, and, in so far as palseontological 

 evidence goes, seem to occupy an intermediate position between the lowest 

 Neocomian and the uppermost Oolites.' 



