242 MESSES. &. W. LAMPLUGH AND J. E. WALKER OK [May 1903, 



out, in varying abundance, with, smooth shining grains of quartz, 

 lydite, and dark iron -oxide ; and occasionally with nests of coarse 

 grit, bits of ironstone, and streaks of bright-green glauconite. At 

 the exterior they are more predominantly gritty, softer, and of a 

 yellow tint ; and their surface is generally lumpy and nodular, being 

 apparently studded with smaller concretions, resembling in this 

 respect the limestone-masses in the * Compound Nodular Band ' at 

 Speeton. They are generally more or less distinctly eroded at the 

 upper surface, and sometimes perforated by borings filled in with 

 dark greensand ; therefore, like the iron-grit bands, they must have 

 been sometimes actually uncovered on the sea-floor. 



The smaller included concretions can often be recognized as the 

 casts of shells, while in other cases they have a spongiform appear- 

 ance. In general aspect these small nodules recall the ' coprolites ' 

 of Up ware and Brickhill ; but in composition they appear to be only 

 sparingly phosphatic, and no phosphatized nodules like those of 

 Potton, Upware, and Brickhill have been found. It is probable, 

 however, that the small nodules may represent an early stage in the 

 production of ' coprolites.' The same species of shells that occur in 

 the condition of limonite in the patches of ironstone-breccia are 

 found also in the calcitic state in the limestone and calcareous grit ; 

 and it is clear that the condition of preservation does not indicate 

 any marked difference of age. Yet. although the limestone-lenticles 

 occur only at one well-defined horizon (as shown in fig. 3, p. 238), 

 we may notice a curious variation in their fossil contents, some 

 blocks containing species in abundance which are rare or absent in 

 other blocks, and almost every mass having its own faunistic in- 

 dividuality, although with certain species common to all. Thus, 

 Septife?' lineatus is very abundant in some blocks and absent from 

 others ; and so with most of the pectens and a few of the brachio- 

 pods, though certain species of the last-mentioned, notably Tere- 

 bratula capillata, are present in nearly every block. Owing to this 

 peculiarity, it is certain that the lists of fossils given on pp. 262-63 

 are not exhaustive, and that as new portions of the deposit are 

 quarried, additions might be made to our collections. 1 



Taken in conjunction with the evidence already given for re- 

 arrangement and winnowing of the sands by current-action, this 

 peculiar distribution of the fossils suggests that the limestone-masses 

 have not been formed quite simultaneously, but that they probably 

 represent shelly patches of the sea-floor where rapid consolidation 

 took place at slightly different times, each locally-indurated patch iu 

 turn remaining fixed when the surrounding incoherent sand was 

 swept away by the changeful currents. Under these circumstances 

 the time-interval between the accretion of contiguous blocks may 



1 It is unlikely, however, that the fossils will be again procurable in such 

 abundance as during our earlier visits ; for at that time the limestone-blocks 

 thrown aside during many years' working of the pits were available on the 

 spoil-heaps, and most of these were broken up during our search. The quantity 

 of this rock exposed in the actual working-faces of the pits at any time is 

 comparatively limited. 



