Vol. 52.] IN YORKSHIKE AND LINCOLNSHIRE. 199 



an exceptionally high percentage of phosphoric acid. 1 After such 

 nodules were formed a local increase in the strength of the current 

 appears often to have wafted away the matrix, and the harder matter 

 was thus exposed to the corrosive action of the sea-water and its 

 denizens, producing on the nodules a misleading appearance of wave- 

 erosion. 



As to the length of the pause in the sedimentation denoted by 

 these bands of nodules, we can judge only from the evidence of 

 other regions where the interval is more fully represented, or from 

 the change to be noted in the fauna of the strata above and below 

 such bands. Jn this particular instance Prof. Pavlow, as already 

 mentioned, believes that an ammonite-zone well developed in Russia 

 is at Speeton condensed into these 4 inches of nodular matter. 



d. The Spilsby Sandstone. 



The lithological and stratigraphical characters of this deposit 

 have already been sufficiently indicated. Where it occurs in the 

 condition of a loose sand the fossils exist only in the form of 

 obscure hollow casts ; but it usually consists in part of irregular 

 concretionary masses, often extremely hard, in which fossils are 

 frequently abundant, though difficult to extract and sometimes 

 injured by crushing. The most prominent feature of the fauna is 

 the abundance of the bivalve mollusca, mainly referable to the 

 genera Pecten, Pinna, Lima, Trigonia, Panopcea, etc., many of 

 which are well preserved. 13 ut a glance at the published lists a will 

 suffice to show the uncertain state of the nomenclature, and as it 

 is not in my power at present to give more precise information 

 regarding these fossils, I do not propose herein to discuss them further 

 than to state that I can recognize among them some forms which 

 occur at Speeton in the ' Pale Beds ' (D 6 and 7) of the zone of 

 Belemnites late rails, and that several species could be matched, I think, 

 in the Hartwell Clay and equivalent Jurassic strata farther south. 3 



1 Considering the clear evidence which we now possess of the alternating en- 

 croachments of a northern and a southern fauna into certain parts of the Nortu 

 European basin during the epoch of the formation of the rocks between the 

 Kimeridge Clay and the Chalk, and the plentiful occurrence of phosphatic 

 nodules where the northern and southern faunas meet, in the compound- 

 nodule band, D 1, at Speeton, the following passage in the Challenger .Report 

 relative to the mode of occurrence of the recent nodules is at least worth 

 noticing (p. 396) : — ' It may be pointed out that phosphatic nodules are 

 apparently more abundant in the deposits along coasts where there are great 

 and rapid changes of temperature, arising from the meeting of cold and warm 



.currents, as, for instance, off the Cape of Good Hope and off the eastern coast 

 of North America. It seems highly probable that in these places large numbers 

 of pelagic organisms are frequently killed by these chauges of temperature, and 

 may in some instances form a considerable layer of decomposing matter on the 

 bottom of the ocean.' 



2 Geol. Surv. Mem. 1887, ' East Lincolnshire,' p. 140 ; H. Keeping. Quart. 

 Journ. Geol. Soc. vol. xxxviii. (1882) p. 241 ; Geol. Surv. Mem., ' Jurassic Rocks 

 of Great Britain,' vol. v. 



3 [Since this paper was read, Prof. Pavlow has described and figured Amelia 

 volge.nsis, Lahus., and Aucella volyensis, var. radiolata, Pavl., both found in the 

 4 zone of Ammonites stenomphalus ' in Russia, from the Spilsby Sandstone of 

 Donnington (see p. 21u). — April 22nd, 1896-1 



