206 ME. G. W. XAMPLUGH ON THE SPEETON SERIES [May 1 896, 



distinct from that of the main mass of the Tealby Clay. And since 

 we know that the Claxby Ironstone extends to the top of this 

 Zateralis-zone, it follows that the clays in question cannot represent 

 a higher horizon than that deposit. These clays, with their accom- 

 panying bands of ironstone, occupy in fact the same position with 

 regard to the Spilsby Sandstone at the southern end of the Wolds 

 as the Claxby Ironstone farther north, and are equivalent in age. 



We are thus brought face to face with an excellent example of 

 that divergence of results which is bound to present itself sooner 

 or later whenever the lithological and the palaeontological characters 

 of a stratified series are independently traced out over an extended 

 area. 



It cannot be denied that throughout Lincolnshire the Spilsby 

 Sandstone and the Tealby Clay, and to some extent also the Claxby 

 Ironstone, form well-defined stratigraphical units, which must be 

 taken by the field geologist as the basis for his work in mapping 

 out the structure of the country. Yet the palaeontological evidence 

 demonstrates that the boundaries of these continuous masses of like 

 material are not strictly isochronous lines, but have had a progres- 

 sive development. 



It seems almost inevitable that in such cases the palaeontologist 

 and the stratigraphist must fix each his own limits independently 

 of the other. The stratigraphist cannot well make use in the field 

 of a line which forsakes a strongly-defined lithological junction 

 to wander vaguely amidst a mass of uniform composition, wherein 

 he could scarcely follow it even were there continuous sections 

 in every direction. The palaeontologist on the other hand is 

 equally compelled to repudiate boundaries obliquely traversing 

 time-limits and life-zones which he seeks above all things to 

 define. 



If we could study the extension of the whole series in an easterly 

 direction, we should probably find this lateral change of lithological 

 character even still more strongly marked. Apparently towards that 

 quarter the various strata would merge into a clayey sequence 

 such as we find at Speeton, as is indicated by the borings east of the 

 Wolds. At Willoughby the full thickness of the Spilsby Sandstone 

 was not proved, but the character of the stratum seems to have 

 become greatly modified, being no longer a clean grit but an 

 * earthy sandstone ' and * ferruginous marlstone,' x while in the 

 Skegness boring already referred to, the Sandstone which is about 

 50 feet thick in the neighbourhood of Spilsby, has thinned away to 

 19 feet, and is associated with clay both above and below ; and 

 the overlying clays have thickened from about 70 to 191 feet. The 

 presence at various horizons in the clay at Speeton of thin, imper- 



1 A. J. Jukes-Browne, Quart. Journ. Geol. Soc. vol. xlix. (1893) p. 467. In this 

 paper a somewhat different reading is given of the Skegness boring from that 

 in the Geol. Surv. Mem. (* East Lincolnshire,' p. 168), and the thickness of the 

 Spilsby Sandstone (including in this term some clayey material) is stated to 

 be 26 feet. At a boring near Driby, if the record is to be trusted, only 4 feet 

 of sand (Spilsby Sandstone) and 4 feet of ironstone (Claxby Ironstone ?) was 

 found between the Tealby Beds and the Kimeridge Clay (ibid. p. 155). 



