Vol. 52.] IN YORKSHIRE AND LINCOLNSHIRE. 195 



Bui, with this reservation respecting the uppermost part, we may 

 safely state the general equivalency of the Upper Kimeridge deposits 

 of Yorkshire and Lincolnshire. 



c. The Basement-bed of the Spilsby Sandstone. 



The base of the pale greenish or reddish quartzose sand or 

 sandstone which overlies the Kimeridge Clay everywhere iu Lin- 

 colnshire southward of Caistor is marked by the presence of 

 numerous dark phosphatic nodules, usually from 1 to 3 inches in 

 diameter. 



At Speeton there is at the same horizon a similar though more 

 compact band of ' coprolites ' (Zone E), and in this respect the two 

 areas are distinctly comparable. These nodules, first noticed as 

 above mentioned, by Mr. H. Keeping in a railway-cutting near South 

 Willingham, were afterwards traced by the officers of the Geological 

 Survey over an extended area, 1 and by them were considered to be 

 derivative pebbles marking the destruction of pre-existing deposits. 

 It appears to me, however, that the derivative character of these 

 nodules is exceedingly doubtful, this view being liable to the same 

 objections as apply under similar circumstances at Speeton. 2 



The composition of the so-called pebbles tells strongly against 

 their derivative origin. Wherever I have been able to examine 

 them they have been of uniform character, without admixture, and 

 have all presented the same dark phosphatic exterior and eroded 

 aspect. But in many instances wheu broken open they reveal a 

 gritty interior not unlike that of the overlying sandstone, and when 

 dissolved in acid they leave an abundant residue of somewhat coarse 

 quartzose sand, which distinctly suggests their original accretion 

 in a sandy matrix like that now enclosing them, and is not 

 to be reconciled with the idea that they were once concretions 

 in the Kimeridge Clay. Moreover at Speeton, where the nodules 

 are enclosed in pyritous clay, the only residue obtained on dissolving 

 them is a little dark fetid mud with groups of angular pyrites- 

 crystals and a very little fine sandy silt. They occur in both 

 localities mostly in the form of more or less obscure casts of shells and 

 portions of the whorls of ammonites, sometimes riddled with the 

 tube-like cavities of boring molluscs ; and these fossils, when 

 recognizable, are distinctly not such as characterize the subjacent 

 strata or any other deposit of a lower horizon now existing in the 

 areas. The specific determination of these casts is of course full 

 of difficulty and uncertainty, as is shown by the state of the lists 

 published in the Geol. Surv. Mems. 3 from the collection made in 

 Lincolnshire by Messrs. A. .]". Jukes-Browne and M. Staniland. The 

 lists contain a total of nineteen determinations ; but in only eight 



1 Mem. Geol. Surv. 1888, ' The Country around Lincoln,' pp. 89 et scqq., and 

 ibid. 1887, 'East Lincolnshire,' pp. 15 et scqq. 



2 • Subdivisions of the Speeton Clay,' Quart. Journ. Geol. Soc. vol. xlv. 

 (1889) p. 586. 



8 ' East Lincolnshire,' p. 139 ; ' Country around Lincoln,' p. 93. 

 Q. J. G. S. No. 20G. p 



